Unit 5

Planet Earth

Topic 1: Minerals

Rocks contain naturally occurring, nonliving crystalline materials called minerals

Most minerals are rare but a few, such as quartz, feldspar, and mica are found throughout Earth’s crust.

A mineral can be an element (a pure substance) or a compound (two or more elements combined)

Minerals

Quartz is an example of a compound as it is made of silicon and oxygen. No other mineral has these elements in the same arrangement and proportions.

Minerals are not only found in rocks, but they are also found in your body.

Moh’s Hardness Scale

Friedrich Mohs developed a scale with 10 values of ‘hardness’ in 1832.

Refer to Hardness Scale in Science Focus 7, page 355, Table 5.1

Diamond is the hardest and talc is the softest.

Crystals There are over 3000 minerals

Crystals are the building blocks of minerals

Crystals occur naturally and have straight edges, flat sides, and regular angles.

There are 6 different crystal types: cubic, tetragonal, hexagonal, orthorhombic, monoclinic, and triclinic

See page 355 in Science Focus 7, Table 5.2

Identification of Minerals

Lustre: this refers to the ‘shininess’ of the mineral (how light is reflected off the surface)

If a mineral shines like a polished metal surface, it is said to have a metallic lustre

If a mineral has a duller shine, it has a non-metallic lustre

Identification of Minerals

Colour: it is the one of the most attractive properties.

Colour can vary within the same mineral. Example: corundum can be white, blue or red depending on what other elements are present.

The mineral corundum (made of aluminum and oxygen) is white when pure. When it contains iron and/or titanium, it is blue (called sapphire). When it contains chromium, it is red (called ruby).

Identification of Minerals

Streak: a streak is the colour of the powdered form of the mineral after it is rubbed across a piece of unglazed porcelain tile.

Look-alike minerals, such as gold and pyrite, can be distinguished using a streak test. Gold leaves a gold streak, while pyrite leaves a greenish-black or brownish-black streak.

A mineral with a greater hardness than the tile will not leave a streak.

Identification of Minerals

Cleavage or Fracture: is the way a mineral breaks apart.

If it breaks along smooth, flat surfaces or planes, it has cleavage

If it breaks with rough or jagged edges, it has fracture

Identification of Minerals

Transparency: it can be transparent (see through), translucent (shadowy), or opaque (non-see through)

Applications

Iron and pyrite are important in the body as it helps the blood carry oxygen

Kidneys produce crystals called kidney stones

Calcium and dolomite help regulate water in body cells

Diamond is used to edge surgical scalpels, razor blades, computer parts, record needles and dentist drills. Diamond-tipped drill bits can cut through steel and rock