Scientists identify minerals according to the following criteria:
- Hardness
- Density
- Specific Gravity
- how its density compares with the density of water
- The density of water is 1.0g/cm3 (1 gram per cubic centimeter of water)
- Color
- Luster
- Streak
- Cleavage/Fracture
- Crystal Shape.
HARDNESS -
Hardness is the ability of a mineral to resist being scratched. To determine
a mineral's hardness, rub the mineral against another known mineral or
object to see if it will become scratched.
The following chart indicates how you might test a mineral for hardness
using a combination of Friedrich Moh's and field hardness scales. 1 represents
the softest mineral while 10 is used for the hardest mineral. A mineral
is able to scratch a mineral with a lower number and can, therefore be
scratched by a mineral with a higher number.
(The links are to photographs of samples of the minerals. Place
your mouse over each image link to view it in a separate window. Close
the window to return to this page and continue.
| Hardness | Item(s) That Will Scratch Mineral | Mineral |
| 1 | Fingernail | Talc |
| 2 | Fingernail | Gypsum |
| 3 | Penny | Calcite |
| 4 | Penny | Fluorite |
| 5 | Glass, Knife blade, or Nail | Apatite |
| 6 | Streak Plate | Feldspar |
| 7 | File | Quartz
(massive type) Quartz crystal |
| 8 | File | Topaz |
| 9 | File/Diamond | Corundum |
| 10 | Diamond |
DENSITY or SPECIFIC GRAVITY-
A mineral's density is the amount of matter in a given space (mass/volume).
Each mineral has a characteristic density (density does not vary with
the size of the mineral). Specific gravity is the ratio of the density
of a mineral compared to the density of water. It is a more specific way
to compare the densities of minerals.
COLOR -
Color is easily observed, but not always a reliable characteristic
for the identification of minerals. A number of different minerals have
the same color.
A mineral may come in a variety of colors or may even change color due
to the environment.
LUSTER -
A mineral's luster describes the way light is reflected from its surface.
Examples of luster include - metallic, nonmetallic, brilliant, glassy,
greasy, pearly, or silky.
STREAK -
The streak of a mineral is the color of the powder left behind when
the mineral is rubbed against a hard, rough surface (e.g. streak plate).
A mineral's streak color may differ from the color of the mineral itself.
This characteristic is most useful for minerals that are relatively soft
(have a hardness less than 7) and which have a characteristic streak color.
CLEAVAGE/FRACTURE -
These two characteristics describes the way a mineral breaks -
*cleavage - means to break along a smooth, definite line
*fracture - refers to rough, uneven breakage
CRYSTAL SHAPE -
Crystal shape results from the pattern formed by the atoms of a mineral
when it is forming. Most minerals have a characteristic geometric shape.
