The Minerals Page
All information on this page was taken from the Geology 101 Laboratory Guide Fourth Edition - George Mustoe
All pictures on this page were taken from Earth, An Introduction to Physical Geology, Fifth Edition - Edward J. Tarbuck and Frederick K. Lutgens
For individual credits for the pictures or information, please consult these books
Before looking at each individual mineral, here are a few things you should know about minerals in general:
Five properties of minerals:
1) minerals must be  naturally occuring
2) minerals must be inorganic
3) minerals must be crystalline solids
4) minerals must have a chemical composition
5) minerals must have characteristic physical properties
The characteristic physical properties of minerals are how we distinguish one mineral from the next.  There are seven properties used to do this:
1)  Luster:  this describes the way that light is reflected from the surface of the mineral - it is most important to determine whether a mineral is metallic or nonmetallic.  After this is distinguished, it is then often a good idea to use other descriptive terms (glassy, milky, waxy).  Keep in mind that there is no official list, these terms are subjective.
2)  Habit:  this refers to the physical form of the mineral.  Is it powdery, blocky, or fibrous?  Again, there is no official list here, you can make your own words up as you go.
3)  Color:  color refers to the presence of trace elements, and is not always a good way to identify a mineral.  Many minerals come in a large variety of colors, this could lead you on an impossible quest for identification if used by itelf.
4)  Streak:  the streak is the color of the mark left behind when a mineral is rubbed or scraped on a surface - this is an indication of the mineral after it has been ground to a fine powder.  This test may not always work, as hard minerals may only scratch the surface instead of leaving a mark.
5)  Reaction with acid:  If a mineral reacts with acid (bubbling) it means that this mineral is calcite (calcium carbonate).  Make sure your body and clothes don't react with the acid - please be careful during this test!!
6)  Fracture and Cleavage:  This describes how a mineral breaks.  If you bang on a mineral with a hammer, you may notice it will break evenly on one or more sides to produce a smooth surface.  If this happens, it is called cleavage.  On the other hand, if the mineral just breaks into a rough surface when hit with a hammer, it is called fracture (fracture can be seen as the absence of cleavage).  A special type of fracture - conchoidal fracture - is when the mineral breaks to produce a pattern of concentric circular lines.  There are several different types of cleavage:
 
 
Cleavage direction Description
 
One cleavage direction sheets or glitter
Two cleavage directions columns
Three cleavage directions cubes (can be rhombic)
Four cleavage directions pyramids
Six cleavage directions dodecahedrons
 
7)  Hardness:  The Moh's scale is the way that is used to rank minerals according to their hardness, which is how hard the minerals are as compared to other minerals and common household objects:
 
Hardness Number Mineral Object Hardness Number Household Object
1 Talc
2 Gypsum 2.5 Fingernail
3 Calcite 3 Copper penny
4 Flourite
5 Apatite 5 Window glass
6 Orthoclase Feldspar 5.5 knife blade (or nail)
7 Quartz
8 Topaz
9 Corundum
10 Diamond
 
Non-Metallic Minerals
Amphibole/Pyroxene Group
(Hornblende Amphibole)
Chemical composition:  complex silicates containing calcium, magnesium and iron
Hardness:  5 to 6
Cleavage:  2 directions (Pyroxenes cleave at 90 degree angles, whereas Amphiboles cleave at angles of about 55 and 125 degrees)
Luster:  glassy
Color:  usually black or greenish brown
    Common Amphiboles:
        Hornblende (pictured) - black or very dark brown
        Tremolite - tan or grey
        Actinolite - usually dark green or greenish brown
    Common Pyroxenes:
        Augite - black or dark brown
        Enstatite - usually brownish green
        Rhodonite - pink (rare, prized as a gem stone)
        Jadeite - jade (rare, very precious)
Feldspar Group
(Plagioclase Feldspar) (Orthoclase Feldspar)
Chemical composition:  aluminum silicates containing aluminum, calcium, and sodium
Hardness:  6
Cleavage:  2 directions
Luster:  glassy or pearly
Color:  usually light colored, opague
    Common Feldspars:
        Plagioclase (pictured) - sodium rich, usually white
        Orthoclase (pictured) - potassium feldspars, usually tan yellow or pink, but sometimes white or green
        Anorthite - calcium feldspar, usually grey
Keep this in mind - Feldspars are very hard to identify because all of their characteristics are very similar, and their colors are highly variable.
Garnet Group
(Garnet crystal embedded in a metamorphic rock)
Chemical composition:  silicates of iron, magnesium, calcium, aluminum, titanium, or chromium
Hardness:  7
Cleavage:  none
Luster:  glassy or resinous
Color:  transparent to translucent, often red or reddish brown, sometimes yellow, green and pink
Like Feldspars, Garnets are often hard to distinguish, as they are very similar.
Quartz Group
(Crystal Quartz - colorless, Amethyst - purple, Citrine - yellow, and Smokey - grey to black)
Chemical composition:  silicon dioxide
Hardness:  7
Cleavage:  none (conchoidal fracture)
Luster:  glassy
Color:  transparent or translucent, often as white masses or colorless hexagonal crystals, however it occurs in many shapes and forms
Mica Group
(Muscovite Mica)
Chemical composition:  complex aluminum silicates containing varying amounts of magnesium, iron, and potassium
Hardness:  2
Cleavage:  1 (forms thin, flexible sheets)
Luster:  shiny
Color:  Biotite Mica is dark brown, while Muscovite Mica (pictured) is usually colorless
Olivine
Hardness:  6.5 - 7
Cleavage:  none
Luster:  glassy
Color:  transparent, usually green or greenish-grey.  After weathering, surfaces can become yellowish or orange because or iron oxidation
Gypsum
Chemical composition:  calcium sulfate
Hardness:  2
Cleavage:  4 directions
Luster:  flat, glassy
Color:  transparent, colorless;  granular lumps are white
Halite
(Halite)
Chemical composition:  sodium chloride
Hardness:  2.5
Cleavage:  3 directions at 90 degrees
Luster:  smooth
Color:  usually occurs as colorless, transparent crystals or white granular masses
Calcite
(Calcite)
Chemical composition:  calcium carbonate
Hardness:  3
Cleavage:  3 directions not at 90 degrees
Luster:  smooth, glassy
Color:  highly variable due to trace elements, but usually clear or light colored
Reacts with acid:  yes
Fluorite
(Fluorite)
Chemical Composition:  calcium fluoride
Hardness:  4
Cleavage:  crystalizes as cubes, however 4 directions of cleavage produce octahedral shapes
Luster:  glassy
Color:  usually transparent green, purple or light blue
Serpentine
Chemical composition:  hydrous magnesium silicate
Hardness:  variable, usually about 4
Cleavage:  none
Luster:  slick, smooth
Color:  greenish or brownish green
Talc
Chemical composition:  hydrous magnesium silicate
Hardness:  1
Cleavage:  none
Luster:  slick, greasy
Color:  greenish grey
Hematite (Earthy Variety)
Chemical composition:  iron oxide
Hardness:  6 or possibly much softer
Cleavage:  none
Streak:  dark rusty red or reddish brown
Color:  reddish
Hematite has the odd ability to occur as a metallic and non-metallic mineral.  See below.
Metallic Minerals
Hematite (Specular Hematite)
Chemical composition:  iron oxide
Hardness:  6
Cleavage:  none
Streak:  dark rusty red or reddish brown
Color:  grey or silver
Hematite has the odd ability to occur as a metallic and non-metallic mineral.  See above.
Magnetite
Chemical composition:  iron oxide
Hardness:  6
Cleavage:  none
Luster:  fuzzy
Color:  dark, grey, metallic-looking
Magnetite is srongly attracted by a magnet.
Pyrite
(Pyrite)
Chemical composition:  iron sulfide
Hardness:  6
Cleavage:  none
Luster:  shiny, metallic
Streak:  brownish-black
Color:  brass-yellow or gold
Pyrite is often referred to as "fool's gold" because it closely resembles gold, but has none of gold's value
Gold
Chemical composition:  gold
Hardness:  2.5 - 3
Cleavage:  ?
Streak:  gold
Color:  yellow
You probably won't need to know much of this for the test, as they try to stay away from the expensive metals in Geology 101...
Galena
(Galena)
Chemical composition:  lead sulfide
Hardness:  2.5
Cleavage:  3 directions at 90 degrees
Luster:  metallic appearance on fresh surfaces, dull flat appearance on weathered surfaces
Color:  silver on fresh surfaces, dull dark grey on weathered surfaces
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