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Martin
Martin, Engineer
Category: General
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Experience:  i'm 41 and i never stopped studying and experimenting
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I do laser engraving work on pieces of slate, there are large

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I do laser engraving work on pieces of slate, there are large chunks of gold in the slate and I am seeing they appear to have square edges which tells me that this would most likely not be real gold. how could a person tell?
Hello and welcome.

It might very well be Pyrite (also known as "fool's gold"). I have one rock in my collection that look just like that:
http://en.wikipedia.org/wiki/File:Pyrite-cubes.jpg
The one you have is less crystalline so it may even look more golden.
The composition is FeS2 so the sulfur can give it the yellow (gold) color. I never personally saw one in sedimentary depot but i know they can also happen there.

It may be hard to do an analysis if the sample are very small. Perhaps the simplest test would be to use a needle to try to damage it. On the Mohs scale, gold is around 2.5 (quite soft) while Pyrite is 6.5 (lot harder).

Take extreme caution with lasers and reflective element like that (also mica), it can reflect with still lot of power in the beam.
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