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I have a bunch of semi-precious stones here, but I am not very learned in geology etc and I would like to have some way to know what kind of stones they are. As far as I understand question about stone identification are considered off-topic here. Is there such a reliable source so I can identify the stones by myself?

Thank you!

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    $\begingroup$ This is a good question! $\endgroup$ – uhoh Feb 26 at 7:16
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Are your stones raw or are they cut & polished as they would appear if mounted in jewellery pieces? There are tests such as streak & hardness which can be done to raw stones but not to polished stones because these test would damage the polished surface.

There are a number of websites that can be used, such as:

Tests that should be done include:

  • Color
  • Luster
  • Hardness - usually involves testing with the blade of a pocket knife or similar
  • Grain size - the size of mineral grains in the stones. If no mineral grains are obvious the stone may be "glassy"
  • Streak - the color left on a piece of white ceramic when the stone is rubbed on the ceramic.
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Is there such a reliable source so I can identify the stones by myself?

Maybe.

Most semi-precious stones are various forms of quartz or silica (e.g., agate, citrine, etc). Quartz is very hard and will scratch glass. It is hard to scratch quartz. Therefore, this is a non-destructive way for identification of quartz. It usually takes a really good polish that lasts. Hardness is pretty much the best way to identify quartz and other varieties of silica, because they visually look all so different.

Apart from quartz, there are several things which are unmistakeable. Watermelon tourmaline, for example. But if you got something which is not quartz and is not obviously something else, it becomes extremely hard to teach yourself to identify it. Even experienced geologists will have a difficult time identifying the stone without resorting to (somewhat) destructive and expensive methods such as XRD, XRF, EDS, etc. The dealers often don't even know what they have. They bought it from someone who bought it from someone and who knows whether the miner actually knows what they're mining.

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As a student in petrology, I would say first you need to know if you gonna cut one thin slice out of this stone/rock, and this is usually how we identify an unknown rock. If so, you can refer to “A Key for Identification of Rock-Forming Minerals in Thin Section” by Andrew J. Barker to get a formal rock identification by observing thin section under optical microscope.

But if your stones are precious, then you might have to rely on observation of your raw samples. Key identifiers usually include :

  • color
  • luster
  • transparency,
  • hardness (using nail and knife)
  • density (weighing by hand)
  • cleavage (tendency to split along definite crystallographic structural planes)
  • mineral fracture (a unique texture and shape of a rock's surface when fractured)
  • mineral shape (sometimes related to crystallographic form, like large quartz crystal)

The details should be easy to found in any textbook of Mineralogy and Petrology. Here is a book-list that I recommended for your reference:

https://bookauthority.org/books/best-rock-identification-books

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mindat.org - * my fav as an avid rockhound/gem junkie

USGS.gov

geology.com

TreasureNet is cool - you send pic (good) in app and the guy returns PDQ

*p.s. --- dont forget *specific gravity test

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