20 Common Minerals
Cochise College  
Virtual Geology Museum             

Geology Home Page

Roger Weller, geology instructor
 wellerr@cochise.edu
copyright 2007-R.Weller


 

1. muscovite mica

5. magnetite

9. azurite

13. milky quartz

17. orthoclase

2. biotite mica

6. hematite

10. malachite

14. rose quartz

18. calcite

3. sulfur

7. galena

11. talc

15. amethyst

19. fluorite

4. pyrite

8. olivine

12. gypsum

16. agate

20. graphite


These minerals can be identified by their distinct physical properties. 
Refer to Photos of Minerals for more visual examples of each of these minerals.

1. muscovite mica
    
Muscovite mica is colorless to a very pale brown in color.  It peels easily into very thin,
flexible, elastic sheets that are nearly colorless. Muscovite is also known as white mica.


2. biotite mica 
     Biotite mica ranges from dark brown to black.  It also peels in very thin, flexible, elastic
sheets like muscovite mica. Biotite is also known as black mica.


3. sulfur 
     Sulfur has a distinctive bright lemon yellow color.  It may be either transparent or
translucent.  Sulfur has no cleavage and will break with a conchoidal fracture (shell-like). 
Sulfur is brittle (breaks easily).  It may also have traces of a sulfury odor.

4. pyrite 
     Pyrite is also known as "fools gold" because it has a yellow metallic color. Pyrite can
be distinguished from native gold by several different properties.  Pyrite is much harder
than gold; it cannot be scratched by a steel straight pin.  Pyrite is brittle; it can be crushed
to a powder, whereas gold simply flattens out because it is a metal. A streak test can also
distinguish pyrite from gold; pyrite produces a greenish black streak and gold produces a
yellow streak.

5. magnetite 
     Magnetite is dark brown to black mineral.  It is easy to identify because it is the only
common mineral that can be picked up by a magnet.  It produces a black streak. 

6. hematite 
     Hematite ranges in color from a powdery brownish red to black to a metallic black.
A black specimen of hematite can closely resemble magnetite, but hematite is not
magnet and it produces a brownish red streak. Powdered hematite is used as rouge.
 


7. galena
     Galena has a metallic luster and is gray in color.  Its most outstanding feature is its
high density; a sample of galena is much heavier than other minerals of the same size. 
Galena is a lead ore.  Galena also has three directions of cleavage at right angles to
each other; it breaks into shiny metallic-looking cubes.

8. olivine 
     Olivine is a transparent to translucent mineral with a distinct yellow green color. 
It often occurs as clusters of small grains in a dark, fine-grained volcanic rock known as
a basalt. Olivine grains only rarely get up to pea-sized. Olivine has not cleavage and
breaks with a conchoidal fracture.  If the material is clear and solid enough, it can be
cut and polished and becomes the gemstone olivine.


9. azurite
     Azurite is a bright blue mineral associated with copper ore. It may occur with green
malachite, also a copper ore.  It is relatively soft at 3.5 on Mohs scale of hardness.

10. malachite
     Malachite is a rich green to dark green copper mineral.  It can occur on its own or
with azurite, a mineral that it is closely related to in chemistry.  It is relatively soft at
3.5 on Mohs scale of hardness.


11. talc
     Talc is the softest mineral; it can be easily scratched with you fingernail. It may
have a pearly luster. Talc is often described as having a greasy or soapy feel to it. 
Talc is commonly white, but can also be a pale green or pale pink. You might get
talc and gypsum confused because they can have similar appearances.


12. gypsum
     Gypsum is a soft, light-colored mineral.  Its color can be colorless and transparent
(selenite) or white, pale pink or pale brown. If crystallized, it displays one direction
of excellent cleavage, but the cleavage fragments are much thicker than those of
mica and the fragments are not elastic. Generally, it lacks the greasy feel of talc.
One form of gypsum tends to form with a fibrous structure (satinspar).


13, 14, 15, and 16 are varieties of the mineral quartz. 

13. milky quartz
    
Milky quartz is white quartz.  The white color comes from carbon dioxide gas
trapped within the quartz structure. Milky quartz is usually massive, but well
well-formed crystals are also common.  In the Huachuca mountains, milky quartz
occurs a a filling material in fractures (mineral veins). All quartz has a hardness of 7
on Mohs scale of hardness and can easily scratch glass. Milky quartz is shiny and
translucent.  Quartz has no cleavage and breaks with a fracture that ranges from
conchoidal to irregular.


14. rose quartz
    
Rose quartz is a variety of massive, translucent quartz with a pink color. It has no
cleavage, it breaks with a conchoidal fracture, and it has a shiny surface. Depending on
quality, it can be used as a gemstone or a decorative garden stone.  Two major
occurrences of rose quartz are Maine and the Black Hills of South Dakota.

15. amethyst
     Amethyst is purple quartz.  It can occur as well-formed quartz crystals in geodes or
deformed crystals in a mineral vein.  If the quality is high enough, amethyst is used as a
gemstone. The luster of amethyst is usually vitreous (shiny).


16. agate
     Agate is a cryptocrystalline variety of quartz; this means that the actual fibers of quartz
are so small that they can barely be seen with a regular microscope.  Agate commonly forms
as a series of colored bands and rough agate has a dull to waxy texture.  Agate polishes to a
high gloss and is a semi-precious gemstone.

17. orthoclase feldspar
     Orthoclase feldspar is a common silicate mineral.  It is responsible for the pink to red
colors found in the igneous rock, granite.  The most common color of orthoclase is salmon
(pinkish orange), but it may also more rarely be white or a pale bluish-green (amazonite).
Orthoclase grains are commonly less than one eighth of an inch. Large, pure pieces of
orthoclase display two directions of cleavage oriented at right angles to each other.
Orthoclase has a hardness of 6 on Mohs scale of hardness and therefore can be scratched
by a piece of quartz
.


18. calcite
     Calcite is a very common mineral. The difficulty in identifying it is that can occur in a
very large variety of colors and forms.  One of the most common forms of calcite crystals
are pointy pyramids that resemble a dog's canine tooth (dogtoothspar).  Large, pure pieces
of crystalline calcite display three directions of cleavage that are inclined (not at 90 degrees). 
Calcite ranges from transparent to translucent.  Colors may be colorless, white, cream, pale
yellow, yellow-brown, brown, and even red due to impurities.  The easiest way to distinguish
calcite is with an acid test; concentrated hydrochloric acid with cause abundant bubbles to
form as it reacts with the calcite.

19. fluorite
    
It is sometimes easy to mistake fluorite for calcite on a quick examination.  However, if
you pay careful attention, fluorite has four directions of cleavage compared to three
directions of cleavage for calcite. Fluorite is also harder than calcite (4 on Mohs scale of
hardness) and can scratch a piece of calcite.  Fluorite is often more colorful than calcite
and can be purple, green, yellow, pink, brown, or colorless and may even show two or more
colors on the same specimen.  Fluorite crystals are usually cubes or octahedrons.  Above
all, fluorite does not fizz in contact with hydrochloric acid.


20. graphite
     Graphite is a very soft, dark gray mineral with a semi-metallic luster. It has a greasy feel
and you can write on a piece of paper with it. It is this last physical property that is
responsible for this mineral being used in pencils.