File:Bcnc.jpg

2026-08-22T11:28:06Z

Cornish semiconductor:

2026-08-05T19:52:56Z

Cornish semiconductor:

File:Main2sc.jpg

2026-08-05T19:50:59Z

Cornish semiconductor:

Marcasite

2026-08-05T15:27:59Z

2026-07-23T21:25:23Z

Cornish semiconductor:

Bassett and Grylls exotic semiconductor field trip

2026-07-22T07:42:02Z

Cornish semiconductor:

Finding your own semiconductors

2026-07-22T07:41:28Z

Cornish semiconductor:

[[Category: ACE R&D]]
[[File:Cut-s.jpg|500px|right]]

=How to find semiconductors in Cornish mine waste=

On the right is an image of a typical Cornish mine dump, this one is at Wheal Prosper, St Hilary. Its been cut through to provide access to a field, and you can clearly see how layers have been deposited - perhaps from different areas of the mine, or different depths, containing different minerals.

The art of collecting minerals from mine waste is known as "fossicking", scanning the surface workings and locating rocks that may contain crystals of interest. We have been running workshops for some time in Cornwall where we take local families out to find crystals. Often the people we do this with have family history in Cornish mining, with plenty of stories to tell and knowledge of the sites we are going to.

A very important resource is [https://mindat.org mindat.org] which contains details of many thousands of mines in the area. I often provide photos and information to this site, [https://www.mindat.org/gallery-83910.html you can see the specimens I have collected here].

==Some documented field trips==

As part of the [[ACE R&D project|Arts Council England R&D project]] I am documenting some trips to search for natural semiconductors in abandoned mine sites around Cornwall:

* [[East Wheal Towan exotic semiconductor field trip]]
* [[Bassett and Grylls exotic semiconductor field trip]]

==What to look for==

Most often in the case of searching for semiconductors, we are looking for metallic mineralisation - the most abundant metal is iron, which is often associated with rarer metals. We are looking for heavy, red or yellow iron stained rocks - often coated in goethite, which is one of the minerals that comprises rust. Usually the most common metallic shiny mineral you'll find is [[pyrite]] or fool's gold, this is a semiconductor - particularly the badly decayed and not well crystallised forms of it.

Many of the mines here were working copper, which is also very abundant, mostly in the form of [[chalcopyrite]]. The copper oxidises and decays into green and blue minerals like malachite and chrysocolla. These are very colourful but not useful for our purposes, however some of these secondary forms, such as [[chalcocite]] (or grey copper) and [[cuprite]] are also great semiconductors themselves.

The other material that Cornwall has become associated with is tin, which was mined for centuries before copper became important. The principle ore of tin is [[cassiterite]] which can also be found in the waste dumps. It is extremely heavy (six times the mass of water) and is also a semiconductor.

Another element that is very common is arsenic, which binds with sulphur to form [[arsenopyrite]] or more rarely oxygen to form [[löllingite]]. These are both great semiconductors.

Lead is fairly common also, in the form of [[galena]] and it's many secondaries. Galena is often found in small patches and veins, material that is courser and richer that can be separated to use with a cat's whisker can be more tricky to find.

Other slightly rarer semiconducting minerals include [[wolframite]] (tungesten ore) which has some interesting properties such as [[negative resistance]].

See also the full [[list of minerals tested]].

It's worth mentioning that while quartz has its own particular place in electronics history (not least in the extraction of silicon) it is not a semiconductor, and not useful for our purposes here.

==Safety==

Use a proper rock hammer to split rocks - normal hammers can splinter dangerously if they are not designed for the purpose. Use eye protection and gloves (all the time), it's quite common for flakes of rock to shoot out at high velocity when hammering (making a sound like a ricocheting bullet in an old film), and the sharp edges of freshly broken quartz can easily cut hands.

Arsenic and lead are toxic, and are contained in a lot of the minerals and rocks in the area. While in the mineralised forms we handle them in they are not massively dangerous - always wash your hands after handling any minerals. If grinding or working dry material wear a good face mask, and use water to avoid any entering your lungs.

Only go to sites that are on public land - not only for aspects of legality (collecting on private land can be permitted sometimes, but it's a more complex situation) but also because these areas are more likely to have their mine shafts well indicated and made safe. Never enter mine workings or old buildings. Often the riskiest aspect of these sites are the mountain bikers we share them with - but we like them because they turn over the ground and expose new rocks!

I take a Geiger counter with me so I can tell if I'm near radioactive rocks. It's rare that this happens, but in some mines the background radiation is noticeably higher, if not at dangerous levels in itself. Uranium ores can be found (very rare and quite valuable) so it's good to know if you need to treat them carefully - or more safely leave them where they are.

ACE R&D project

2026-07-22T07:40:11Z

Cornish semiconductor: /* 26/06/26 */

==21/07/26==

The [[Bassett and Grylls exotic semiconductor field trip]], possibly found [[magnetite]] and tested previously found specularite [[hematite]]. To my surprise this form of hematite from this location is a semiconductor, while material from elsewhere is not. Also a positive result from [[magnetite]].

==14/07/26==

Decided to CNC cut the [[chaos triangle]] module, using some new expensive end mills from Germany, very nice cuts but broke 2 doing half the board. Went back to old ones to finish.

Short range AM transmitter arrived in the post, ended up listening to a few hours of 20s Jazz on the [[Junior crystal radio]]! I used a small powered Adafruit amplifier circuit driving a 8 ohm speaker. Tried the original galena crystal and one from Wheal Clinton, both worked well, and the range (a few tens of centimetres) seemed to increase gradually over time. I used a few metres of wire for the arial and no grounding on either the transmitter or crystal radio.

Started work on the variscan [[low pass gate]] PCB, fixing the reversed pins which were a mistake in the design. Managed to short the power and it damaged the battery connectors, not the actual circuit (which took over an hour to figure out).

==09/07/26==

Too hot to explore mine sites, mostly experimenting with new feedback ideas, prototyped a new [[chaotic relaxation]] circuit. The theory being that the nonlinear effects of these natural semiconductors can be compounded via feedback. Also arranging two East Wheal Towan tracks and documenting the [[squarewave]] module.

==06/07/26==

Uploaded [[chaotic triangle]]/Wheal Clinton galena/1920s radio video to instagram, and spent a few hours jamming and recording with exclusively East Wheal Towan samples using the [[Variscan Synthesis|variscan synth]] for the first time since the Sheffield gig. Native copper find was confirmed on mindat, so finished report on the [[East Wheal Towan exotic semiconductor field trip]].

==01/07/26==

Writing up yesterdays work and adding to the site. Managed to find some [[molybdenite]] in a bucket of material from Penlee beach, hoping I can get a [[Semiconductor curve traces|curve trace]] from one of these microscopic grains.

==30/06/26==

Spent a morning doing curve traces and an afternoon getting the new "Junior" crystal radio integrated into an experimental [[chaotic triangle]] circuit.

Discoveries:
* [[Wolframite]], is in fact not a semiconductor (or a conductor) at least not at the voltages I'm using, as it has extremely high resistance. Not sure if what I measured before was a mistake (perhaps a specimen coated in something else) or if it varies with specimens. But neither my (beautiful) sample from Wheal Fortune, nor the magnetically extracted detritus from a crushed Poldice mine specimen provided any results.
* Silver cat's whiskers are too conductive to work well with pyrite, chalcopyrite or arsenopyrite, but work really well with galena and quite well with chalcocite. This means, as expected - that minerals need matching with cat's whisker materials.
* The East Wheal Towans specimens seem strange, the galena seems different to galena elsewhere and the chalcopyrite and arsenopyrite was very reluctant to work.
* The galena sample that came with the Junior radio is excellent, and the radio makes it easy to swap out different crystals.
* The chaotic triangle is capable of making very interesting sounds on it's own in combination with a crystal. Getting a PCB made for this is next on the list.

Adding [[CERN Open Hardware Licence Version 2 – Strongly Reciprocal]] everywhere before I start uploading loads of circuit diagrams etc.

==28/06/26==

Posted [[Razor blade diode]] video to instagram and got a zillion views and comments. It's good because it clearly shows the difference between two types of mineral.

==26/06/26==

[[East Wheal Towan exotic semiconductor field trip]] to East Wheal Towans, Great Wheal Charlotte and Nangiles mine. Specifically looking [[cuprite]] from Porthtowan area, and [[wolframite]] from Nangiles mine near Bissoe.

==25/06/26==

Release of live Sheffield recording (as a free download) on bandcamp, soundcloud and archive.org

Had a good morning doing R&D:

* Rebuilt crystal diode triangle voice on breadboard from the [[log synth]], added feedback to make it into a [[chaotic triangle]] circuit.
* Tried building a [[Razor blade diode]] and tested it in the triangle voice (made another video).
* Quickly tried a [[Perikon diode]] with some zincite purchased from Poland and [[chalcopyrite]] from Ale & Cakes Mine.

==14/06/26==

Live performance at Sheffield Pattern Club!

==13/06/26==

Tried again, and posted a 1920s crystal diode making noise video on instagram and had 200 likes and 7,848 views. This seems to be a good way of doing 'outreach' for this project at the moment.

==12/06/26==

Getting the [[Variscan Synthesis]] live rig working.

* Replaced all 0.1uF DC blocking capacitors to 1.0uF, removed unwanted low pass filtering.
* Using silver cat's whiskers after reading about galena point contact diodes.
* Added crystal radio diode, see [[semiconductor history]].
* Using new portable 6 channel mixer to replace 4 track recorder.
* Lots of rehersals and recordings made.

==03/06/26==

Received crystals, cat's whiskers and tins & posted them on instagram, video had 6,500 views which was a surprise!

==01/06/26==

Project announcement and added/working on [[semiconductor history]] and [[cat's whisker setups]] after questions on mastodon. A sizable proportion of the materials budget might be going on ebay purchases of crystal radio parts!

==30/05/26==

Starting a log here of the work done. The first entry is things I said I'd do so I can keep a check on it (chopped up from proposal)!

End up with unique sounds and electronic music created with instruments I will create designed to work with natural semiconductors collected from Cornish mine waste.

* The music itself will document the specific locations and history of the site the material comes from (who worked there e.g. the Bal Maidens, stories we know of the site, its industrial heritage, etc.
* The instruments will be artworks in their own right
* I will use the time to research more interesting and complex musical potential.
* The aim will be to create instruments that focus on this that highlight raw materials using Cornish granite, soldered copper pipes, CNC milled copper circuit boards alongside the semiconducting minerals themselves.
* test these new sounds and prototype instruments in a live setting
* develop existing and new collaborations within this community and further afield
* The instruments would also be designed to be used by other people in future

All sounds, music and designs created will be published online as creative commons and open hardware for others to follow and provide feedback.

{| class="wikitable" style="margin:auto"
|+ Project plan from proposal
! Start !! End !! Task
|-
| 02/05/2026 || 31/07/2026 || Researching history of semiconductor development from early 1900's
|-
| 02/05/2026 || 01/09/2026 || Researching mine history and searching mine sites for semiconducting material
|-
| 01/06/2026 || 30/10/2026 || Prototype instrument experiments based on research
|-
| 01/06/2026 || 31/10/2026 || Music making and test performances
|-
| 01/09/2026 || 31/10/2026 || Documentation, publishing recordings, blog posts
|}

I've started by [[semiconductor history|looking into the history of semiconductor usage]].

[[Category:ACE R&D]]

ACE R&D project

2026-07-22T07:39:06Z

Cornish semiconductor: /* 06/07/26 */

==21/07/26==

The [[Bassett and Grylls exotic semiconductor field trip]], possibly found [[magnetite]] and tested previously found specularite [[hematite]]. To my surprise this form of hematite from this location is a semiconductor, while material from elsewhere is not. Also a positive result from [[magnetite]].

==14/07/26==

Decided to CNC cut the [[chaos triangle]] module, using some new expensive end mills from Germany, very nice cuts but broke 2 doing half the board. Went back to old ones to finish.

Short range AM transmitter arrived in the post, ended up listening to a few hours of 20s Jazz on the [[Junior crystal radio]]! I used a small powered Adafruit amplifier circuit driving a 8 ohm speaker. Tried the original galena crystal and one from Wheal Clinton, both worked well, and the range (a few tens of centimetres) seemed to increase gradually over time. I used a few metres of wire for the arial and no grounding on either the transmitter or crystal radio.

Started work on the variscan [[low pass gate]] PCB, fixing the reversed pins which were a mistake in the design. Managed to short the power and it damaged the battery connectors, not the actual circuit (which took over an hour to figure out).

==09/07/26==

Too hot to explore mine sites, mostly experimenting with new feedback ideas, prototyped a new [[chaotic relaxation]] circuit. The theory being that the nonlinear effects of these natural semiconductors can be compounded via feedback. Also arranging two East Wheal Towan tracks and documenting the [[squarewave]] module.

==06/07/26==

Uploaded [[chaotic triangle]]/Wheal Clinton galena/1920s radio video to instagram, and spent a few hours jamming and recording with exclusively East Wheal Towan samples using the [[Variscan Synthesis|variscan synth]] for the first time since the Sheffield gig. Native copper find was confirmed on mindat, so finished report on the [[East Wheal Towan exotic semiconductor field trip]].

==01/07/26==

Writing up yesterdays work and adding to the site. Managed to find some [[molybdenite]] in a bucket of material from Penlee beach, hoping I can get a [[Semiconductor curve traces|curve trace]] from one of these microscopic grains.

==30/06/26==

Spent a morning doing curve traces and an afternoon getting the new "Junior" crystal radio integrated into an experimental [[chaotic triangle]] circuit.

Discoveries:
* [[Wolframite]], is in fact not a semiconductor (or a conductor) at least not at the voltages I'm using, as it has extremely high resistance. Not sure if what I measured before was a mistake (perhaps a specimen coated in something else) or if it varies with specimens. But neither my (beautiful) sample from Wheal Fortune, nor the magnetically extracted detritus from a crushed Poldice mine specimen provided any results.
* Silver cat's whiskers are too conductive to work well with pyrite, chalcopyrite or arsenopyrite, but work really well with galena and quite well with chalcocite. This means, as expected - that minerals need matching with cat's whisker materials.
* The East Wheal Towans specimens seem strange, the galena seems different to galena elsewhere and the chalcopyrite and arsenopyrite was very reluctant to work.
* The galena sample that came with the Junior radio is excellent, and the radio makes it easy to swap out different crystals.
* The chaotic triangle is capable of making very interesting sounds on it's own in combination with a crystal. Getting a PCB made for this is next on the list.

Adding [[CERN Open Hardware Licence Version 2 – Strongly Reciprocal]] everywhere before I start uploading loads of circuit diagrams etc.

==28/06/26==

Posted [[Razor blade diode]] video to instagram and got a zillion views and comments. It's good because it clearly shows the difference between two types of mineral.

==26/06/26==

[[Porthtowan/Nangiles exotic semiconductor field trip]] to East Wheal Towans, Great Wheal Charlotte and Nangiles mine. Specifically looking [[cuprite]] from Porthtowan area, and [[wolframite]] from Nangiles mine near Bissoe.

==25/06/26==

Release of live Sheffield recording (as a free download) on bandcamp, soundcloud and archive.org

Had a good morning doing R&D:

* Rebuilt crystal diode triangle voice on breadboard from the [[log synth]], added feedback to make it into a [[chaotic triangle]] circuit.
* Tried building a [[Razor blade diode]] and tested it in the triangle voice (made another video).
* Quickly tried a [[Perikon diode]] with some zincite purchased from Poland and [[chalcopyrite]] from Ale & Cakes Mine.

==14/06/26==

Live performance at Sheffield Pattern Club!

==13/06/26==

Tried again, and posted a 1920s crystal diode making noise video on instagram and had 200 likes and 7,848 views. This seems to be a good way of doing 'outreach' for this project at the moment.

==12/06/26==

Getting the [[Variscan Synthesis]] live rig working.

* Replaced all 0.1uF DC blocking capacitors to 1.0uF, removed unwanted low pass filtering.
* Using silver cat's whiskers after reading about galena point contact diodes.
* Added crystal radio diode, see [[semiconductor history]].
* Using new portable 6 channel mixer to replace 4 track recorder.
* Lots of rehersals and recordings made.

==03/06/26==

Received crystals, cat's whiskers and tins & posted them on instagram, video had 6,500 views which was a surprise!

==01/06/26==

Project announcement and added/working on [[semiconductor history]] and [[cat's whisker setups]] after questions on mastodon. A sizable proportion of the materials budget might be going on ebay purchases of crystal radio parts!

==30/05/26==

Starting a log here of the work done. The first entry is things I said I'd do so I can keep a check on it (chopped up from proposal)!

End up with unique sounds and electronic music created with instruments I will create designed to work with natural semiconductors collected from Cornish mine waste.

* The music itself will document the specific locations and history of the site the material comes from (who worked there e.g. the Bal Maidens, stories we know of the site, its industrial heritage, etc.
* The instruments will be artworks in their own right
* I will use the time to research more interesting and complex musical potential.
* The aim will be to create instruments that focus on this that highlight raw materials using Cornish granite, soldered copper pipes, CNC milled copper circuit boards alongside the semiconducting minerals themselves.
* test these new sounds and prototype instruments in a live setting
* develop existing and new collaborations within this community and further afield
* The instruments would also be designed to be used by other people in future

All sounds, music and designs created will be published online as creative commons and open hardware for others to follow and provide feedback.

{| class="wikitable" style="margin:auto"
|+ Project plan from proposal
! Start !! End !! Task
|-
| 02/05/2026 || 31/07/2026 || Researching history of semiconductor development from early 1900's
|-
| 02/05/2026 || 01/09/2026 || Researching mine history and searching mine sites for semiconducting material
|-
| 01/06/2026 || 30/10/2026 || Prototype instrument experiments based on research
|-
| 01/06/2026 || 31/10/2026 || Music making and test performances
|-
| 01/09/2026 || 31/10/2026 || Documentation, publishing recordings, blog posts
|}

I've started by [[semiconductor history|looking into the history of semiconductor usage]].

[[Category:ACE R&D]]

Porthtowan/Nangiles exotic semiconductor field trip

2026-07-22T07:38:28Z

Cornish semiconductor: Cornish semiconductor moved page Porthtowan/Nangiles exotic semiconductor field trip to East Wheal Towan exotic semiconductor field trip

#REDIRECT [[East Wheal Towan exotic semiconductor field trip]]

East Wheal Towan exotic semiconductor field trip

2026-07-22T07:38:28Z

Cornish semiconductor: Cornish semiconductor moved page Porthtowan/Nangiles exotic semiconductor field trip to East Wheal Towan exotic semiconductor field trip

[[File:Gwcharlotte-panorama.jpg|frame|View from East Wheal Towan of the remaining engine house of Great Wheal Chalotte on the left, and Wheal Coates on the right]]

One of the tasks I've been funded to do is "Researching mine history and searching mine sites for semiconducting material", and for the first trip of this project I decided to head to the north coast to check out a few places, these are a bit further away than the mines in the Gwennap area that I'm mainly been exploring and so are likely to have different mineralogy, and thus perhaps different sounding semiconducting mine waste minerals:

* [https://www.mindat.org/loc-216211.html East Wheal Towan]
* [https://www.mindat.org/loc-216208.html Charlotte United Mine]
* [https://www.mindat.org/loc-210320.html Great Wheal Charlotte]

These are all within a short walk of each other near the cliffs between Porthtowan and Chapel Porth beach.

== East Wheal Towan ==

East Wheal Towan turned out to be quite abundant in minerals, I think because it's a minor site that not many people have been to (added to the fact it's surrounded in very prickly gorse I had to carry our dog over). Most of the minerals I found had very coarse crystallisation with nicely formed (euhedral) faces.

[[File:Eastwhealtowan-mix.jpg]]

This is a rock I found containing [[arsenopyrite]], [[galena]] and sphalerite all hosted inside a matrix of well formed quartz and green chlorite. None of these are rare, but it's satisfying to find all of them in one small sample - and given that previously there were no confirmed minerals listed on the [https://www.mindat.org/loc-216211.html mindat.org locality] it means I could add them all in one go.

The sharply defined silver crystals are arsenopyrite, the darker clusters on the top left and lower middle are galena and the grey mass on the right above the vein of silver arsenopyrite is sphalerite.

[[File:EastWhealTowan-chalcopyrite.jpg]]

I also found plenty of good material here for some [[semiconductor curve traces]], firstly a small piece of sharply defined milky quartz with bright chalcopyrite that had survived weathering in between the quartz faces. This is quite noisy, as is common with chalcopyrite and pretty leaky, but with a defined corner where it start conducting well over 1V:

[[File:Ewtowan-chalcopyrite.png|center]]

There was also a lot of arsenopyrite as usual, this was from a mass similar to the photo above, and it behaves pretty strangely - it is very tricky to find a junction, and when I did it was quite extreme. I've never seen arsenopyrite have such a sudden threshold as this:

[[File:Ewtowan-arsenopyrite.png|center]]

There was also quite a lot of galena, I took some curve traces from a thin vein which has broken away so you can access the galena on multiple sides running through the rock. Testing it with a multimeter it's electrically connected all the way through (registering a few Kohms across the piece). This provides another unusual curve - like an exponential, usually galena has clearer thresholds. I'm not sure if this is something to do with the thin section, or perhaps its interaction with arsenopyrite which is also present. The interaction of different semiconducting minerals that have grown together is another avenue of research I haven't managed to follow yet, perhaps looking closer at the [[Perikon diode]] may lead to some experiments around that.

[[File:Ew-towan-galena.png|center]]

This is plenty to make some music specific to East Wheal Towan in the future, and it does seem to have some interesting peculiarities to explore.

== Charlotte United Mine ==

I spotted where I think this mine must have been from the footpath, a small cluster of trees often seems to mark the location of a mine shaft - small trees seem to like growing right on top of backfilled shafts. Unfortunately it would have meant another trip through even deeper prickly gorse - and it was much further away from the path, so I decided to give this one a miss and press on.

== Great Wheal Charlotte ==

The trail to Great Wheal Charlotte is lined with what I would guess possibly are the remains of a tramway that would have been used to carry away the ore - densely packed heavily mineralised ironstained rocks look like they could have supported the tracks, but it might just be the remains of a road. The remains of the engine house (only one wall remains) is a good signpost, and the mine waste dumps are pretty extensive here.

[[File:Gw-charlotte.jpg]]

Although a much larger site, it's quite hard to find mineralised rocks - one indicator is the red colour of the area in the photograph, this is coming from the copper, cuprite in fact. There was also a lot of malachite here, bright green spots and veins in white quartz. This indicates a lot of carbonates in the rock, and was entirely absent in East Wheal Towan, about half a kilometre away.

Other than a piece of [[arsenopyrite]] from the track way and some glittery pyrite not usable as a semiconductor as it was too disseminated in the matrix, I found it difficult to find much - the one thing I did find however was quite something.

[[File:Gwcharlotte-copper.jpg]]

[[File:Gw-charlotte-native-copper.png|right]]

This is native copper, and it's quite rare to find in it's elemental form - this is the first time I've found any. It was in a dark druzy tourmaline rock just under the surface at the base of the dump shown in the photograph above. It's comprised of a thin layer that has solidified in a fracture of the host rock, and has nearly all converted into red [[cuprite]] and green malachite. This is the largest fragment, but in other chunks of this rock the copper has lifted away from the surface and you can bend it.

I had hopes that I would be able to get a curve trace from the cuprite coating the copper, but unfortunately it seems impossible. I'm not entirely clear why, but if the cuprite is not connected together electrically than it would make sense that this would be difficult as I have to use two cat's whiskers to connect to the small fragments. The copper itself conducts very happily of course, I include a curve trace so at least there is one on this site of a normal conductor for reference.

[[Category: ACE R&D]]

Finding your own semiconductors

2026-07-22T07:37:48Z

Cornish semiconductor:

[[Category: ACE R&D]]
[[File:Cut-s.jpg|500px|right]]

=How to find semiconductors in Cornish mine waste=

On the right is an image of a typical Cornish mine dump, this one is at Wheal Prosper, St Hilary. Its been cut through to provide access to a field, and you can clearly see how layers have been deposited - perhaps from different areas of the mine, or different depths, containing different minerals.

The art of collecting minerals from mine waste is known as "fossicking", scanning the surface workings and locating rocks that may contain crystals of interest. We have been running workshops for some time in Cornwall where we take local families out to find crystals. Often the people we do this with have family history in Cornish mining, with plenty of stories to tell and knowledge of the sites we are going to.

A very important resource is [https://mindat.org mindat.org] which contains details of many thousands of mines in the area. I often provide photos and information to this site, [https://www.mindat.org/gallery-83910.html you can see the specimens I have collected here].

==Some documented field trips==

As part of the [[ACE R&D project|Arts Council England R&D project]] I am documenting some trips to search for natural semiconductors in abandoned mine sites around Cornwall:

* [[Porthtowan/Nangiles exotic semiconductor field trip]]
* [[Bassett and Grylls exotic semiconductor field trip]]

==What to look for==

Most often in the case of searching for semiconductors, we are looking for metallic mineralisation - the most abundant metal is iron, which is often associated with rarer metals. We are looking for heavy, red or yellow iron stained rocks - often coated in goethite, which is one of the minerals that comprises rust. Usually the most common metallic shiny mineral you'll find is [[pyrite]] or fool's gold, this is a semiconductor - particularly the badly decayed and not well crystallised forms of it.

Many of the mines here were working copper, which is also very abundant, mostly in the form of [[chalcopyrite]]. The copper oxidises and decays into green and blue minerals like malachite and chrysocolla. These are very colourful but not useful for our purposes, however some of these secondary forms, such as [[chalcocite]] (or grey copper) and [[cuprite]] are also great semiconductors themselves.

The other material that Cornwall has become associated with is tin, which was mined for centuries before copper became important. The principle ore of tin is [[cassiterite]] which can also be found in the waste dumps. It is extremely heavy (six times the mass of water) and is also a semiconductor.

Another element that is very common is arsenic, which binds with sulphur to form [[arsenopyrite]] or more rarely oxygen to form [[löllingite]]. These are both great semiconductors.

Lead is fairly common also, in the form of [[galena]] and it's many secondaries. Galena is often found in small patches and veins, material that is courser and richer that can be separated to use with a cat's whisker can be more tricky to find.

Other slightly rarer semiconducting minerals include [[wolframite]] (tungesten ore) which has some interesting properties such as [[negative resistance]].

See also the full [[list of minerals tested]].

It's worth mentioning that while quartz has its own particular place in electronics history (not least in the extraction of silicon) it is not a semiconductor, and not useful for our purposes here.

==Safety==

Use a proper rock hammer to split rocks - normal hammers can splinter dangerously if they are not designed for the purpose. Use eye protection and gloves (all the time), it's quite common for flakes of rock to shoot out at high velocity when hammering (making a sound like a ricocheting bullet in an old film), and the sharp edges of freshly broken quartz can easily cut hands.

Arsenic and lead are toxic, and are contained in a lot of the minerals and rocks in the area. While in the mineralised forms we handle them in they are not massively dangerous - always wash your hands after handling any minerals. If grinding or working dry material wear a good face mask, and use water to avoid any entering your lungs.

Only go to sites that are on public land - not only for aspects of legality (collecting on private land can be permitted sometimes, but it's a more complex situation) but also because these areas are more likely to have their mine shafts well indicated and made safe. Never enter mine workings or old buildings. Often the riskiest aspect of these sites are the mountain bikers we share them with - but we like them because they turn over the ground and expose new rocks!

I take a Geiger counter with me so I can tell if I'm near radioactive rocks. It's rare that this happens, but in some mines the background radiation is noticeably higher, if not at dangerous levels in itself. Uranium ores can be found (very rare and quite valuable) so it's good to know if you need to treat them carefully - or more safely leave them where they are.

Bassett and Grylls exotic semiconductor field trip

2026-07-22T07:35:20Z

Cornish semiconductor:

File:Bassett Grylls main.jpg

2026-07-22T07:21:48Z

Cornish semiconductor:

Chalcopyrite

2026-07-22T07:14:08Z

Cornish semiconductor:

[[File:EastWhealTowan-chalcopyrite.jpg|thumb|right|frame|Unusually well formed chalcopyrite from East Wheal Towan, Porthtowan]]
[[File:Ewtowan-chalcopyrite.png|right|frame|A curve trace of chalcopyrite from East Wheal Towan]]

* Lustre:Metallic
* Transparency:Opaque
* Colour:Brass yellow, often with an iridescent tarnish.
* Streak:Greenish black
* Hardness:3½ - 4 on Mohs scale
* Tenacity:Brittle
* Cleavage:Poor/Indistinct Indistinct on {011}, sometimes distinct.
* Fracture:Irregular/Uneven

[https://www.mindat.org Data from mindat.org]

Chalcopyrite is the main ore of copper, is softer than pyrite and fairly easy to find in usable quantities. It's rarely well crystallised, but forms thick veins and large blobs, usually in quartz.

Due to the copper content it has a very low overall resistance, I find it one of the easiest minerals to find good semiconducting junctions, it doesn't seem to alter much with oxidisation or weathering. Unlike [[pyrite]] it doesn't seem to vary much between sites or occurrences. As you can see in the curve trace, it's particularly susceptible to noise - during performances I tend to start with chalcopyrite or [[chalcocite]] as they are particularly 'eager' low resistance semiconductors compared to some [[galena]] or [[cassiterite]].

Famously it was combined with zincite to build bi-crystal [[Perikon diode|"Perikon" detectors, invented in 1908 by Greenleaf Whittier Pickard]].

===Pages mentioning chalcopyrite===

{{Special:WhatLinksHere/Chalcopyrite}}