These are the
characteristics or properties of minerals:
Luster:
What does the surface of the mineral look like? It could be
metallic or non-metallic. It either shines [or has a dull
shine] like you expect in metals. An example of this
is aluminum. The mineral might be
non-metallic. There are lots of words to describe the
surface shine of a non-metallic mineral. Some are: waxy
[like a candle], dull [is not shiny], or pearly [shimmery or
iridescent]. There are a lot of other words that we
included in the actual mineral descriptions and we
explained each one.
Hardness:
The Mohs Scale of Hardness is used to explain how hard a
mineral is. Hardness ranges from 1 [soft] to 10 [hard].
Since a mineral can only be scratched by something that is
harder than it is, its place on the Mohs Scale is usually
explained with a description of the thing that will scratch
it. A mineral that is higher in number on the scale, will
scratch anything that has a lower number. For example,
Topaz that is an 8 on the scale will scratch Talc that is a
1. On the other hand, Topaz won't scratch a diamond
that is a number 10. Gemstones are always harder
minerals. Even though there are other pretty minerals,
they are not used as gemstones unless they are hard.
Gemstones cost a lot of money and if they were soft, they
would break easier. The gemstones couldn't
be used for jewelry if they were soft. On the chart
below, the gemstones are higher numbers since they are
harder.
scratch.wmv [1098
KB]
To download: Right click on the link above and highlight
"Save target as".
The hardness scale is not a normal scale with
even changes from one number to another. It looks more
like the diagram to the right. You can see that the
numbers from one to seven are evenly spaced apart. This
means that it is a gradual rise in hardness from one to two,
from three to four, and so on. But when you get to the
hardest part of the scale, the hardness increases a lot.
This means that there is a big difference in the hardness of a
diamond, for example, that is a 10 on the scale and a mineral
that is nine. If you didn't see a diagram like the one on
the right, you wouldn't know that there were such big
differences between the numbers.
Color:
Mineralogists know what colors the minerals usually are. An
example of this is the diamond. After studying diamonds for
years and years, scientists can say, from experience, that
diamonds are usually colorless, yellow, or grey. They also
know that they can be other colors, too. Color is only one of
the characteristics that they use to identify a mineral.
Because there are differences in minerals [like colors],
mineralogists don’t depend on just one of the
characteristics to figure out which mineral it is. They use
them all.
Streak:
This is the color of the dust that is left after you grind
up a mineral. In school, we usually use something called a
streak plate because we can’t just pound all the minerals
into dust to test streak. Instead, we rub the mineral on
the ceramic plate which has a hardness of 7. Any mineral
that is softer than 7 will leave a little dust on the plate
when it is rubbed on it. The color of the dust is a mineral
characteristic. Sometimes the color of the dust is
different than the color of the mineral.
Cleavage:
Cleavage is how a mineral splits. Some minerals split
evenly in one direction into sheets, like
Mica. Other
minerals always split in three or four directions. The
mineral does the same split every time. If you had 2000
chunks of Mica, every one would split in one direction into
thin sheets. Because it happens every time, it is a way to
identify a mineral.
Fracture:
When a mineral shatters, it doesn’t always break evenly like
cleavage. It fractures into different shapes depending on
what mineral it is. Some have jagged edges, some have
smooth ones, and some break into grains or uneven chunks.
Mineralogists expect certain minerals to
fracture into jagged pieces because they always do.
Magnetism:
Mineralogists will check to see if the mineral is magnetic
or not. If it is attracted to a magnet, it is
magnetic. If it is not attracted to a magnet, it isn't
magnetic. This is another
way to identify a mineral.
Specific Gravity:
This is the weight of the mineral compared to the weight of
water. This tells the scientist how heavy a mineral is.
For example:
platinum is very, very heavy. Mineralogists
are able to narrow down what the mineral is based on
its weight. Metals are heavier than regular minerals.
Crystal system:
There are lots of different crystal formations. A mineral
always has the same one. With each mineral, we named the
crystal system with its proper name and then our team artist
drew a picture of what the crystal looks like. We felt this
would be easier to understand than axes, prisms, and
symmetry.
Transparency:
Most minerals are transparent, translucent, or opaque.
Transparent means that light can shine straight through it.
An easier description is that you can see right through it
like you do with window glass. Translucent means that
light can shine through it but its path is changed when it
exits. An easier description is that it is blurry to
look through. Opaque means that light won't go through
it at all. Our easier description is that you can't
see through it at all.
The hardness scale is not a normal scale with
even changes from one number to another. It looks more
like the diagram to the right. You can see that the
numbers from one to seven are evenly spaced apart. This
means that it is a gradual rise in hardness from one to two,
from three to four, and so on. But when you get to the
hardest part of the scale, the hardness increases a lot.
This means that there is a big difference in the hardness of a
diamond, for example, that is a 10 on the scale and a mineral
that is nine. If you didn't see a diagram like the one on
the right, you wouldn't know that there were such big
differences between the numbers.