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[[File:Chalcocite.jpg|thumb|right|frame|Chalcocite from Wheal Virgin, Gwennap]] | [[File:Chalcocite.jpg|thumb|right|frame|Chalcocite from Wheal Virgin, Gwennap]] | ||
[[File:Chalcocite-penstruthal.png|right|frame|A curve trace of | [[File:Chalcocite-penstruthal.png|right|frame|A curve trace of chalcocite from Penstruthal mine]] | ||
[[File:Prosper-chalcocite-silver-uptriangle.jpg|right|frame|A very similar curve trace of chalcocite from Wheal Prosper (this was using a silver cat's whisker)]] | |||
* Lustre:Metallic, Sub-Metallic | * Lustre:Metallic, Sub-Metallic | ||
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* Comment:Somewhat sectile | * Comment:Somewhat sectile | ||
[https://www.mindat.org | [https://www.mindat.org Data from mindat.org] | ||
Chalcocite is also called "grey copper", and is an important ore of copper. It's fairly common, but tends to be more common as isolated crystals. Thick veins can be found, usually in a dense and 'massive' (finely crystallised) nature. It can look a bit like weathered sphalerite, but tends to be associated with green crusts of malachite and blue crysocolla. | Chalcocite is also called "grey copper", and is an important ore of copper. It's fairly common, but tends to be more common as isolated crystals. Thick veins can be found, usually in a dense and 'massive' (finely crystallised) nature. It can look a bit like weathered sphalerite, but tends to be associated with green crusts of malachite and blue crysocolla. | ||
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It has a similarly low overall resistance as chalcopyrite - but it tends to have a very sudden and distinct point at which it starts conducting (around +1.3V), and when it does, it can carry large currents. Interestingly it can display properties of a [https://en.wikipedia.org/wiki/Shockley_diode Shockley diode], in that once 'switched on' it will remain in a conducting state until a much lower threshold (near to 0V) is reached. | It has a similarly low overall resistance as chalcopyrite - but it tends to have a very sudden and distinct point at which it starts conducting (around +1.3V), and when it does, it can carry large currents. Interestingly it can display properties of a [https://en.wikipedia.org/wiki/Shockley_diode Shockley diode], in that once 'switched on' it will remain in a conducting state until a much lower threshold (near to 0V) is reached. | ||
Due to these interesting characteristics, it tends to be a favourite of mine. I find it better performing than most [[galena]], easier to find junctions and less leaky - as this fairly typical curve shows, completely flat in the negative portion. It also seems to | Due to these interesting characteristics, it tends to be a favourite of mine. I find it better performing than most [[galena]], easier to find junctions and less leaky - as this fairly typical curve shows, completely flat in the negative portion. It also seems to be less likely to invert with different point contacts, as galena is prone to. | ||
==Visualising Shockley diode characteristics== | |||
Usually we use a sawtooth wave to generate curve plots, sweeping from -2.5 to 2.5 volts and then snapping back to -2.5 volts again. If we use a sine wave instead, we can see the difference between the voltage sweeping up and then down, and so see how this 'switching on and off' characteristic happens (I have no idea why chalcocite does this, and e.g. [[chalcopyrite]] does not). | |||
[[File:Prosper-chalcocite-silver-sine.png]][[File:Prosper-chalcocite-steel-sine.png]] | |||
The loops visible here are where the voltage rises, it takes the lower path, at some point jumping up as current floods through the crystal. Then once 'on' and the voltage drops down, it continues to allow current the flow at a higher rate than the same voltage when it was going the other direction. It stays like this until it reaches nearly zero volts, when the current stops flowing again and the crystal is 'turned off'. | |||
===Pages mentioning chalcocite=== | ===Pages mentioning chalcocite=== | ||
{{Special:WhatLinksHere/Chalcocite}} | {{Special:WhatLinksHere/Chalcocite}} | ||
Latest revision as of 21:47, 12 September 2026
- Lustre:Metallic, Sub-Metallic
- Transparency:Opaque
- Colour:Blue black, gray, black, black gray, or steel gray
- Streak:Blackish lead gray
- Hardness:2½ - 3 on Mohs scale
- Tenacity:Brittle
- Cleavage:Poor/Indistinct Indistinct on (110)
- Fracture:Conchoidal
- Comment:Somewhat sectile
Chalcocite is also called "grey copper", and is an important ore of copper. It's fairly common, but tends to be more common as isolated crystals. Thick veins can be found, usually in a dense and 'massive' (finely crystallised) nature. It can look a bit like weathered sphalerite, but tends to be associated with green crusts of malachite and blue crysocolla.
It has a similarly low overall resistance as chalcopyrite - but it tends to have a very sudden and distinct point at which it starts conducting (around +1.3V), and when it does, it can carry large currents. Interestingly it can display properties of a Shockley diode, in that once 'switched on' it will remain in a conducting state until a much lower threshold (near to 0V) is reached.
Due to these interesting characteristics, it tends to be a favourite of mine. I find it better performing than most galena, easier to find junctions and less leaky - as this fairly typical curve shows, completely flat in the negative portion. It also seems to be less likely to invert with different point contacts, as galena is prone to.
Visualising Shockley diode characteristics
Usually we use a sawtooth wave to generate curve plots, sweeping from -2.5 to 2.5 volts and then snapping back to -2.5 volts again. If we use a sine wave instead, we can see the difference between the voltage sweeping up and then down, and so see how this 'switching on and off' characteristic happens (I have no idea why chalcocite does this, and e.g. chalcopyrite does not).
The loops visible here are where the voltage rises, it takes the lower path, at some point jumping up as current floods through the crystal. Then once 'on' and the voltage drops down, it continues to allow current the flow at a higher rate than the same voltage when it was going the other direction. It stays like this until it reaches nearly zero volts, when the current stops flowing again and the crystal is 'turned off'.