Mineral Groups
Major Silicates
More than 90% of the minerals in Earth’s crust are members
of the silicate family. A silicate is a compound of silicon,
oxygen, and usually one or more metallic elements, such as
aluminum or iron. In all silicates, the basic building block is
the silica tetrahedron, consisting of four oxygen atoms
bonded to central silicon atoms.
Figure 1. Three ways of drawing the silica
tetrahedron: a) At left, a ball & stick model,
showing the silicon cation in orange
surrounded by 4 oxygen anions in blue; b)
At center, a space filling model; c) At right,
a geometric shorthand.
Quartz
Quartz is made entirely of tightly bound silica tetrahedral. It
has the chemical formula SiO2.
Some Physical Properties of Quartz:
 glassy or greasy lustre
 colourless or white (pure quartz)
 can be rose coloured, amethyst, and smoky
 exhibit either conchoidal or irregular fracture
 hardness of 7 on Mohs scale (hardest of the common
minerals)
Some uses of quartz include being used in watch
movements, prisms, heat lamps, glass, and paints. The
crystal quartz is a semiprecious gemstone often worn as
jewellery.
Quartz is found in granite and is the second most abundant
family of minerals.
Feldspars
The feldspar family of minerals makes up 60% of Earth’s
crust.
Some Physical Properties of Feldspars:
 two directs of cleavage
 hardness of 6
 pearly lustre
Feldspar differs from quartz because aluminum atoms
replace some of the silicon atoms in the silica tetrahedra.
The replacement creates a net electrical charge in these
tetrahedral, which is balanced by the addition of other
metals, such as potassium, sodium, or calcium. Because of
this feldspars are classified into two major groups –
potassium feldspars and sodium-calcium feldspars.
The most common potassium feldspar is orthoclase (lightcoloured – pink or salmon, cleavage surfaces meet at right
angles, commonly found in granite) and the most common
sodium-calcium feldspar is plagioclase (white to gray,
cleavage surfaces meet at slightly less than a right angle,
one cleavage surface is often marked by fine parallel lines
called striations).
Some uses of feldspar include being used in glass and
ceramics.
Other Silicates
Pyroxene Family
 have cleavage surfaces that meet nearly at right angles
 Augite (ferromagnesian silicate) is the most common
member of this family
 Augite is dark in colour
 Augite has two good cleavages and a hardness
between 5 and 6
Mica Family
 hardness of 2.5 and perfect cleavage
 can easily be picked out of rocks such as granite and
gneiss
 form flat crystals
 cleave in only one direction
Amphibole
 complex silicates that form long, needlelike crystals
 most common amphibole is hornblende
 hornblende can be shiny dark green, brown, or black
 hardness from 5 to 6
 has two good cleavages that meet at oblique angles
 ferromagnesian silicate
 found in igneous and metamorphic rocks
Olivine
 olive-green colour
 hardness of 6.5 and glassy
 shell-like fracture
 some meteorites contain olivine
 ferromagnesian silicate
Kaolinite
 aluminum silicate
 formed by the weathering of feldspars and other
silicates
 white
 hardness of about 2
 perfect cleavage in one direction
Carbonates
Summarize the information on Carbonates in the chart below
(page 110).
Minerals
Description
General Information
Calcite
Dolomite
Oxides and Sulfides
Summarize the information on Oxides and Sulfides in the
chart below (pages 110 -111).
Minerals
Description
General Information
Hematite
Magnetite
Pyrite