ben86
starting to shine!
Member since December 2019
Posts: 30
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Post by ben86 on Jan 5, 2020 9:59:49 GMT -5
selenite? and greywacke?
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fuss
spending too much on rocks
Member since October 2018
Posts: 250
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Post by fuss on Jan 5, 2020 12:10:28 GMT -5
Satin Spar, gypsum.
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fuss
spending too much on rocks
Member since October 2018
Posts: 250
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Post by fuss on Jan 5, 2020 12:13:57 GMT -5
Need a higher resolution image of your second rock to help.
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rockstock
spending too much on rocks
Member since April 2019
Posts: 472
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Post by rockstock on Jan 5, 2020 13:18:05 GMT -5
Granite type rock with quartz lines/veins?
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NevadaBill
fully equipped rock polisher
Member since January 2019
Posts: 1,332
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Post by NevadaBill on Jan 9, 2020 13:36:30 GMT -5
I vote Gypsum too. I find a lot of that in the washes here in Nevada. But almost never as nice as that large bar you got there. I like how they reflect light. I tried to grind some on a wheel, but they are soft as butter, and difficult to get a shine on. Here are some of my attempts. I have little bowls of these chunks all over the yard.
Again, I like how they reflect light, which is difficult to see in a picture.
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Post by rockpickerforever on Jan 9, 2020 14:18:17 GMT -5
I vote Gypsum too. I find a lot of that in the washes here in Nevada. But almost never as nice as that large bar you got there. I like how they reflect light. I tried to grind some on a wheel, but they are soft as butter, and difficult to get a shine on. Here are some of my attempts. I have little bowls of these chunks all over the yard.
Again, I like how they reflect light, which is difficult to see in a picture.
Bill, the way the scratches look, especially on that trapezoidal shaped one, in the center, makes me think calcite. Not to mention, calcite crystals are trapezoidal in shape.
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Post by rockpickerforever on Jan 9, 2020 20:49:16 GMT -5
I vote Gypsum too. I find a lot of that in the washes here in Nevada. But almost never as nice as that large bar you got there. I like how they reflect light. I tried to grind some on a wheel, but they are soft as butter, and difficult to get a shine on. Here are some of my attempts. I have little bowls of these chunks all over the yard. Again, I like how they reflect light, which is difficult to see in a picture.
This is the chunk of calcite I have. Not self collected, it came from a rock show or the swap meet.
It's kind of rhomboid shaped, or maybe a parallelogram? Google tells me it is a rhombohedron. But do you see what I mean about the scratches?
Pretty sure gypsum, calcite and selenite are closely related. Looked up their chemical composition. They are very similar, although they do have their differences.
Calcite - CaCO3 Gypsum - CaSO. 4· 2H2O. Selemite - CaSO4 · 2H2O
Similar Anhydrite (CaSO4)
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NevadaBill
fully equipped rock polisher
Member since January 2019
Posts: 1,332
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Post by NevadaBill on Jan 12, 2020 13:59:21 GMT -5
Interesting. That Calcite that you have looks like better material than mine. I think I just got a bunch of soft, dumb, semi-clear rocks.
Thank you for helping us out to identify the materials we have.
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Post by rmf on Jan 12, 2020 19:47:44 GMT -5
As rockpickerforever noted that is selenite (CaSO4), it has a Mohs hardness of 2. This is the same as satin spar. The only other mineral it could be is Ulexite (NaCaB5O6(OH)6·5H2O but I have never seen Ulexite that long. The hardness of Ulexite is Mohs 2.5. Ulexite is Triclinic crystal and Selenite is Monoclinic crystal. As adjectives the difference between triclinic and monoclinic is that triclinic is (crystallography) having three unequal axes all intersecting at oblique angles while monoclinic is (crystallography) having three unequal axes with two perpendicular and one oblique intersections.
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