Mineral:
A mineral is a natural, inorganic solid formed in the earth. An
inorganic substance is one that is not made up of living things
or the remains of living things.
1. each mineral has a characteristic chemical composition
2. either an element or a compound
3. most rocks are composed of mixtures of diff. minerals.
Identification of a mineral (must be yes to each ?)
1) is it inorganic?
2) does it occur naturally in the earth?
3) is it a solid?
4) does it have definite chemical composition?
Kinds of minerals:
2000 kinds of minerals are found in the earth’s crust.
Rock forming minerals: of the 20 of these minerals, 10 are so
common they make up 90% of the mass of the earth’s crust
They are: quartz, orthoclase, feldspar, plagioclase feldspar,
mica, calcite, clay, dolomite, halite, gypsum, and ferromagnesian
minerals(which include olivines, pyroxenes, and amphiboles.
-All minerals can be classified into two main groups based on their chemical composition- silicate minerals and nonsilicate minerals.
Silicate Minerals:
-1. all contain atoms of silicon and oxygen (quartz is composed
of only these two elements)
-2. most silicate minerals contain one or more other kinds of
atoms ---3.feldspar is the most common silicate mineral. The type
of feldspar mineral formed is dependent on which metal combines
with the silicon and oxygen atoms.
Thus the type of metal that combines with silicate determines
that type of feldspar it is.
******Feldspar and quartz alone make up more than 50% of the crust!
Nonsilicate minerals:
-1. 4% of the crust consists of nonsilicate minerals (lack silicon)
-2. classified into 5 major groups based on their chemical comp:
carbonates, halides, native elements, oxides, sulfates, and sulfides.
Almost all minerals have a crystalline structure. Each type of crystalline material is characterized by a specific geometric arrangement of its atoms or ions. Crystalline material will sometimes form a crystal, a natural solid substance that has definite shape.
Identification of Minerals:
Based on specific characteristics or properties:
1. Color-not a very reliable char., key is to look at a
freshly exposed surface
2. Streak-the color the mineral in powered form., rub it
against a ceramic tile and see what color the streak is
3. Luster- the light reflected from the mineral. Minerals
that reflect light like polished metal have metallic luster.
other types of luster: glassy (transparent minerals), waxy, pearly,
and brilliant (diamond)
4. Cleavage and Fracture:
Cleavage-refers to the splitting of a mineral along smooth, flat
surfaces. it is related to the types of bonds in the internal
structure of the mineral. Minerals have specific patterns that
they cleave into-this can be used to identify them.
Minerals that do not break along cleavage planes, tend to fracture,
or break, unevenly into curved or irregular pieces.
Types of fractures are based on their appearance: uneven or irregular,
splintery or fibrous, and curved or conchoidal.
5. Hardness-the ability of a mineral to resist scratches.
It differs from resistance to cleavage or fracture. ie a diamond
is the hardest mineral and yet it can be split quite easily along
cleavage planes.
The hardness of a mineral is determined by the strength of the
bonds between the atoms or ions that make it up.
-We determine by using a hardness scale called the Moh’s
scale (1-10). Softest mineral is talc and is given a value 1 and
diamond is the hardest and is given a value of 10.
The hardness test is a scratch test-what scratches what. A #5
mineral will scratch a #4, but not a #6 mineral.
6. Crystal Shape: mineral crystals have one of 6 basic
shapes. are 1-Cubic or Isometric (axes at = lengths at 90 degree
angles
2-Triclinic (3 axes are of un= length and are oblique to one another)
3-Hexagonal (3 horizontal axes are the same length and intersect
at 60 degree angles, vertical axis is longer or shorter than the
horizontal axes)
4-Orthorhombic (3 axes of different lengths, intersect at 90 degree
angles
5-Monclinic (of 3 axes of different lengths, 2 intersect at 90
degree angles and the 3rd is oblique to the others)
6-Tetragonal (3 axes intersect 90 degree angles; 2 horizontal
axes are of equal length; the vertical axis is longer or shorter
than the horizontal axes.
7. Density: the ratio of the mass of a substance to its volume.
Unusual Properties of Minerals:
1-Magnetism:
2-Flourescence- the ability to glow under ultraviolet light. They
absorb UV light then produce visible light of various colors.
3-Radioactivity-