STUDY GUIDE FOR MINERAL TEST – MONDAY NOVEMBER 24
Minerals are naturally occurring, inorganic solids with a distinct pattern and
chemical formula.
When a mineral breaks along an even surface it is called cleavage. When it breaks
unevenly it wants fracture.
Calling something a crystal, means that it has an internal arrangement of atoms. It
does not necessarily have to have sparkle to be considered a crystal.
On the earth, there are nine common minerals that form all of the rocks. There are
several hundred other minerals but they are found separate from rocks. Most rocks
have a number of minerals in common.
Over 90% of all minerals on earth are in the silicate family. When a mineral
contains the elements silicon and oxygen, it is a silicate. The two most common
minerals on the Earth, quartz and feldspar, are silicates. Quartz is the most common
mineral in beach sand. Most of the minerals in igneous rocks are silicate minerals.
Biotite mica is a silicate with cleavage in one direction (it peels).
Tourmaline, amethyst and kyanite are silicate minerals with beautiful crystals.
Hardness is the resistance of a mineral to scratching
Physical tests such as hardness, streak and cleavage are used to determine the
identity of a mineral.
The Moh’s Scale of Hardness goes from 1-10 with one as the softest and ten as the
hardest.
The hardness scale: !) Talc 2) Gypsum 3) Calcite 4) Fluorite 5) Apatite 6) Feldspar
7) Quartz 8) Topaz 9) Corundum 10) Diamond
A fingernail has a hardness of 2.5 Glass has a hardness of 5.5
A mineral’s luster describes how it reflects light. In general there are two categories
– metallic and non-metallic. In the non-metallic group there are quite a few lusters
including: adamantine (sparkly), glassy, silky, greasy, resinous, dull or earthy.
The density of a mineral is its mass divided by its volume
The streak of a mineral is the color of the powder left behind when it is rubbed
against a streak plate (unglazed porcelain). Pyrite, a golden mineral, has a greenishblack streak. Hematite, a dark silvery mineral, leaves a reddish brown streak.
Minerals like gold, copper and sulfur are called native elements because they are
each made up of just one kind of element or atom.
Limestone and marble, which is metamorphosed limestone, are comprised of the
mineral calcite. Calcite is calcium carbonate. It is the mineral that fizzes when a
drop of hydrochloric acid is put on it (an acid-base reaction). Rhodochrosite and
malachite are also carbonates but they do not fizz with hydrochloric acid.
Most of the mineral ores (extracted and use for industry) are from the sulfide family.
Galena is a sulfide mineral and is a major source of lead.
Gypsum and Borax are salt minerals that formed as evaporate deposits. This means
as a body of water evaporated (due to climate change) salts are left behind.
Calcite and fluorite can appear as different colors and their crystals are both glassy.
You could tell them apart by using the hardness test.
Rubies and sapphires are in the mineral group called corundum. Corundum,
whether or not gem-quality, has a hardness of 9. Rubies and sapphires that are not
gem quality are used in cutting tools, sandpaper and nail files.