Copper
Photo by
Patrick Laird ©
Copper
Photo by
Patrick Laird ©
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Copper Photo by Patrick Laird © |
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Copper Photo by Patrick Laird © |
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The first thing noticed about a mineral is its
color. It is sometimes helpful in identifying a mineral, but shouldn't
be the basis for identification. Some minerals are consistently one
color, such as malachite, which is green. Although malachite is always
green, some minerals such as fluorite can be green or any other color.
There are a couple of reasons why minerals such as fluorite or quartz have
different colors. One reason for the wide varieties of color are
impurities. These impurities are too small to change the composition
of the mineral, but do effect the color. Another reason for different
colors is the atomic structure. As light enters the atomic structure,
some of the light is absorbed and some of it is reflected, leaving a distinct
color. (Chesterman)
Photo by Patrick Laird © |
Photo by Patrick Laird © |
Photo by Patrick Laird © |
Photo by Patrick Laird © |
The streak of a mineral is the true color of the mineral and is quiet helpful in identifying minerals. It is easiest to rub the mineral across a streak plate in order to view the powdered residue (streak). The best streak plates are unglazed white porcelain tiles. This allows you to view the color of the mineral against a white background. If a mineral has a hardness greater than 6.5, it will not leave a streak (Chesterman) |
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Luster refers to the way a minerals surface reflects
light.
Luster is best observed on a freshly broken surface of the mineral and
can sometimes help you identify a mineral. There are two groups of
luster, metallic and non-metallic. Within these groups there are
a number of different kinds of luster. There are a few minerals that
have a sub-metallic luster, such as sphalerite. The terms listed
in the table below are used as descriptive terms only. (Chesterman)
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| Hardness refers to two things when working with minerals. One, it reflects the atomic structure of a mineral and two, it is the mineral's resistance to being scratched. The hardness of a mineral is a major physical property used to help identify minerals. Hardness is measured using the Mohs Hardness Scale (table on the right) with number 1, talc, being the softest to number 10, diamond, being the hardest. A few items that are easy to use are a fingernail, with a hardness of 2.5 and glass, with a hardness of about 5.5. Remember that hardness is the resistance to being scratched and not the resistance to being hit with a hammer. (Schumann) |
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Specific gravity is used to identify minerals, but more often in a laboratory
than in the field. The specific gravity of a mineral is the weight
of that mineral compared to the weight of the same volume of water.
Specific gravity can also be determined as the density of a mineral.
Minerals that have a low specific gravity will seem light while minerals
with a high specific gravity will seem heavy (Schumann). Metallic
minerals will have a higher specific gravity than nonmetallic minerals.
Using specific gravity is narrowed down to a few select minerals in the
field. The average specific gravity for a metallic mineral is about
5.5, while 2.5 is the average for a nonmetallic mineral.
ESU Specimen Collection Photo by Patrick Laird © |
Barite has a specific gravity of about 4.5, which makes it extremely heavy for a nonmetallic mineral and also makes it easy to identify by holding it in your hand. |
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Created by Patrick Laird for GO336 Mineralogy at Emporia State University, November 11, 2002.
copyright 2002 Patrick Laird. All rights reserved.
