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Educationspecific gravity/ hardness question for mineral

10th Nov 2017 16:58 UTCMatt Courville

Good day,

Does it seem reasonable to have an anhydrite crystal with:

Specific Gravity: 3.09 (average)

Hardness: >3.5 and <5.5

- due to an impure mixture of another mineral such as apatite, boracite, or pargasite?

10th Nov 2017 17:39 UTCReiner Mielke Expert

Could you show us a picture of it?

10th Nov 2017 18:17 UTCMatt Courville

This is a photo from a thread that got somewhat convoluted. I have since tested the two properties listed. The larger crystal is the one in question.

10th Nov 2017 18:58 UTCKevin Conroy Manager

Cancrinite?

10th Nov 2017 20:11 UTCOwen Lewis

Matt,

How did you get the SG? Break off a piece of the 'crystal in question' - or what? 3.09 is too high for anhydrite, especially as an averaged result. Your hardness result is also way too high. Why the range? were you testing in different directions? The tables I rely on give 3.0 - 3.5 as the reliable range for anhydrite.

If it were mine, I would not be happy assigning an ID just on the basis of these results :-(

10th Nov 2017 20:23 UTCMatt Courville

Hi Owen, so the story goes:

1) I think that I collect some rough, odd-looking apatite ('nothing to write home to mom about')

2) after inquiring on the odd crystal shape, I have to re-think what I have (I seem to be confusing everyone)

3) I took a number of other crystal fragments from the same site with the same composition and did some tests.

The range on hardness is due to it scratching or not scratching various minerals and hardness items. It has been suggested to me that it may be a mixture of two minerals which seems fair enough, so I thought to ask here. I agree that it doesn't add-up for anhydrite alone.

10th Nov 2017 22:15 UTCMatt Neuzil Expert

Where was this collected? That could give some insight. To me it appears purple and colour is not the best property for identifying, it is hard to tell wat the matrix is composed.

10th Nov 2017 23:16 UTCReiner Mielke Expert

Does concentrated HCl have any effect on it?

12th Nov 2017 17:45 UTCMatt Courville

Concentrated HCl does not dissolve the crystal (threw-in a few different pieces). It does slightly etch the outer surface similar to apatite - which I added in one piece to the HCl to compare as a reference.

12th Nov 2017 18:57 UTCReiner Mielke Expert

Failing further testing, such as a phosphate test using ammonium molybdate, seems to me apatite would be a good bet.

13th Nov 2017 00:46 UTCMatt Courville

Thanks Reiner, and everyone earlier. This brings my initial question back, so I will try to word it best.

Geologically speaking, could apatite take on a non-hexagonal form? Could this be a previously altered mineral to apatite? If so, is there any visual examples out there; perhaps even beyond mindat?

Thanks,

Matt

13th Nov 2017 12:05 UTCReiner Mielke Expert

Apatite does not always form recognizable crystals. It can be anhedral. Your specimen looks somewhat like a breccia so it may be a fragment of a crystal with no faces.

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