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Other tips » | Desert
Safety | Household
Tips | Identify
Rocks |
Identifying Rocks & Minerals
Here are some tests you can perform
to help you identify your rock and mineral specimens.
| First,
examine your specimen with a magnifying glass and take note
of its outside appearance.
We recommend acquiring either Rocks,
Minerals & Gemstones or A Field Guide to North American Rocks & Minerals to help
identify whether your find is a 'mineral' or a 'rock'.
Use a Mineral Testing Kit. Your kit should include a streak plate (for color test),
glass plate (for hardness test), plastic dropper bottle (for acid
test), a magnet and 5/10X magnifier. |
|
Once you have
identified your sample you can proceed accordingly.If you have identified your specimen as a 'mineral' you
should look for the mineral's transparency. If you can see through
the specimen, it is transparent. If light can pass through, but
the specimen cannot be seen through, your mineral is translucent.
Minerals that do not let light through are called opaque.
Mohs Scale of Mineral Hardness
In 1812 the Mohs scale of mineral hardness was devised by the German mineralogist
Friedrich Mohs (1773-1839), who selected the ten minerals because they were common or
readily available. The scale is not a linear scale, but somewhat arbitrary.
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.) |
Hardness of some other items:
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.
Our page Household
Hints on Care of Granite and Marble
countertops and floors offers
some good advice about treatment and protection of these.
For more tips
on every subject imaginable
Looking for more scales?
Scales Directory is the site for any kind of scale you can think of!
Comments? Questions? Suggestions?
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