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Please help to identify this stone

0 votes

Please help me to identify this stone plus a rough value if possible.  I do not know where this stone is from,  I discovered it hidden away in brown paper inside an air vent of a old truck I bought.

asked Mar 30, 2016 by Brenda1 (140 points)
edited Apr 6, 2016 by Brenda1

3 Answers

0 votes
Once again, I would like to see a few better pictures. The husk appears to be limestone. One picture of the inside material, well focused and a shot of both sides would be most helpful.
answered Mar 30, 2016 by Weasel (40,320 points)
0 votes
Brenda, take a metal nail file and see if you can mark the stone. It appears to be Quartz or chalcedony. We need to know how hard it is. Most precious stones will not scratch, but glass and a few other minerals will.
answered Apr 1, 2016 by Weasel (40,320 points)
If I try to scratch it with a metal file, it only makes a white powder as if I'm filing my nails.  I tried to grind it as well but it does not crack,  it made the surface smooth however.
0 votes
Determining Hardness

Original Mohs Scale of Mineral Hardness

The relative hardness of minerals is determined according to Mohs Scale, named after the German mineralogist, Friedrich Mohs (1773-1839), who devised it in 1812. In the original Mohs Scale, ten minerals were arranged in order of increasing hardness and were assigned the numbers one to ten. These ten minerals are shown in the first column of the table below:

Hardness

Mineral

Associations and Uses

1

Talc (Softest)    Talcum powder. (can be scratched by a fingernail.)
2

Gypsum    Plaster of paris.
Gypsum is formed when seawater evaporates from the Earth's surface. (May be scratched by a fingernail or by a copper coin.)
3

Calcite    Limestone and most shells contain calcite.
(Can be scratched by a steel pocket knife or sometimes a copper coin. Will scratch a fingernail, may scratch a copper coin.)
4

Fluorite    Fluorine in fluorite prevents tooth decay.
(Can be scratched by a steel pocket knife. Will scratch a fingernail and a copper coin.)
5

Apatite    When you are hungry you have a big "appetite".
(Can be scratched by a steel pocket knife. Will scratch a fingernail and a copper coin.)
6

Orthoclase    Orthoclase is a feldspar, and in German, "feld" means "field".
(Will not scratch glass but will scratch steel blades, copper coins & fingernails.)
7

Quartz     (Will scratch glass, steel blades, copper coins & fingernails.)
8

Topaz    The November birthstone. Emerald and aquamarine are varieties of beryl with a hardness of 8. (Will scratch glass, steel blades, copper coins & fingernails.)
9

Corundum    Sapphire and ruby are varieties of corundum. Twice as hard as topaz.
(Will scratch glass, steel blades, copper coins & fingernails.)
10

Diamond (hardest)    Used in jewelry and cutting tools. Four times as hard as corundum.
(Will scratch all of the above.)

A substance with a higher Mohs number is capable of scratching a substance with a lower number.
Mohs selected these ten minerals because they were common or readily available. The scale is not a linear one, and is somewhat arbitrary. For example, Fluorite at four is not twice as hard as Gypsum at two; nor is the difference between Calcite and Fluorite similar to the difference between Corundum and Diamond.

Hardness is used in a rough way to inform mineral identification in the field. Real minerals out in the field can look remarkably alike. This may be due to weathering, variations in their chemical structure from the ideal, or clathrate inclusions that simply change the colour of the mineral. Sometimes faulting and metamorphism can induce facets and planes in a mineral that aren't natural to it, so that the mineral looks like another.

The Mohs scale is still used today although it has been extended, putting diamond at 15, to accommodate newly-developed materials of extreme hardness which lie between 10 and 15.

The Extended Mohs Scale

Mohs Substance

Hardness

Liquid

1
Substance as indicated in the standard scale

2-6
Vitreous pure silica

7
Quartz

8
Topaz

9
Garnet

10
Fused zirconia

11
Fused alumina

12
Silicon carbide

13
Boron carbide

14
Diamond

15
Some common field tests:

2.5

Fingernail (will scratch 1-2 hardness)
2.5-3

Gold, Silver
3

Copper penny
4-4.5

Platinum
4.5

Iron
5.5    Knife blade
6-7    Glass
6.5    Iron pyrite
7+    Hardened steel file

On each level of the scale a mineral can be scratched by something of the same or higher level, but nothing lower.

Match the hardness table above with the items listed below it. Test your mineral specimen by trying to scratch it with your fingernail. If it doesn't scratch, next try a copper penny. If you are able to scratch your specimen with the penny but not with your fingernail, it has a hardness between 2.5 and 3.5. If the specimen does not scratch with a penny, try a knife blade or glass. A diamond can only be scratched by another diamond.


One last test that is commonly used is called a streak test.
A mineral's "streak," or color when it is finely powdered, is always the same, even when the color of the mineral varies. (The color of the streak can be very different from the color of the mineral itself.) Rub your specimen across a piece of porcelain tile (a "streak plate") and examine the color it leaves behind. Once you have performed your tests, compare your results with a Rocks and Minerals field guide to come to a final identification of your specimen.
answered Apr 2, 2016 by Weasel (40,320 points)
The one picture makes me think this sample might fluoresce under ultraviolet light. If so, it could indicate flourite.
If it was calcite it would react vigorously with acids. Vinegar and visine are very mild acids. If those do not work you can use a stronger acid but be careful to work in a ventilated area, outdoors is best, and use protective equipment: gloves and goggles.

The pictures seem to be of more than one rock...
The pictures are of one rock all pictures were taken the same time,  the ones where the fluorescence is showing was taken under a normal led flashlight.  I took it to a jeweler who did the diamond test and it is not a diamond,  I took it to our local gem and crystal dealer and she said it's a normal piece of glass, so I came home and hit the rock with a steel hammer,  I am posting a picture of what the hammer did to the rock,  which make me think it's definitely not glass, apparently the rock absorbs heat according to the lady that helped me, it was body temperature when I took it out of my jacket pocket.

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