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Identity HelpNeed help identifying this green transparent mineral

7th Sep 2019 22:51 UTCIan Monk

Hello! Hoping someone here can help me with this one. Hardness is around 5, it can easily scratch fluorite, and is easily scratched by apatite. Mostly transparent. This specimen has a rhombic cross-section, shown in the additional photos. I've had this in my collection for many years, and unfortunately I don't remember exactly how or where I got it. A couple more images below. Thank you!

EDIT: to clarify, it does also scratch apatite. They can scratch each other.

https://imgur.com/MzV9evL

https://imgur.com/IOdGQ6T

8th Sep 2019 00:29 UTCPaul Brandes 🌟 Manager

Welcome to Mindat, Ian!

My first thought was fluorapatite.

8th Sep 2019 00:47 UTCWilliam W. Besse Expert

Looks to me more like the kyanite from Vitória da Conquista, Bahia, Brazil .

Bill

8th Sep 2019 01:06 UTCIan Monk

Wow, I think you nailed it! I didn't even consider kyanite because I've never seen it in green, but the color, the transparency, crystal shape, and termination on those specimens from Brazil look very, very similar. Thank you!

8th Sep 2019 01:16 UTCPaul Brandes 🌟 Manager

Only issue with Kyanite is that Apatite should not scratch it.

Still, they do appear very similar...

8th Sep 2019 01:33 UTCIan Monk

I should have worded that differently. It does actually scratch the apatite sample I was using, but barely.

8th Sep 2019 02:03 UTCRuss Rizzo Expert

oops...

8th Sep 2019 03:11 UTCHarold Moritz 🌟 Expert

Careful because kyanite has two different hardnesses depending on how you scratch it. It is H5 parallel to the length of the crystals, but is H7 at right angles to this direction. So if you used an apatite (H5) to scratch it the long way, which I think most people would naturally do anyway, then your result is valid and the ID likely.

8th Sep 2019 03:13 UTCAlan Pribula

Kyanite is unusual in that its hardness is significantly different in different directions. (An alternate name for it is 'disthene,' meaning 'two strengths,' reflecting these two different hardnesses.) Testing the hardness parallel to the long axis of the crystal and also perpendicular to that axis should prove to be a fairly definitive test to either confirm or rule out kyanite.

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