Earth's Crust: Rocks, Minerals, and Elements

• A rock is a naturally formed group of minerals bound together, consisting of one or more minerals in varying quantities.
• A mineral is a naturally occurring inorganic solid with a distinct chemical composition and crystalline structure.
• Approximately 4000 minerals exist, including quartz, halite (table salt), mica, calcite, gold, and diamond.
• All rocks and minerals in the Earth’s crust are made of elements.
• An element is a substance composed of chemically alike atoms that cannot be broken down by ordinary methods.

Abundance of Elements in Earth's Crust

• Eight major elements make up 98.5% of the Earth's crust total mass.
• Oxygen makes up 46.6%.
• Silicon makes up 27.7%.
• Aluminum makes up 8.1%.
• Iron makes up 5.0%.
• Calcium makes up 3.6%.
• Sodium makes up 2.8%.
• Potassium makes up 2.6%.
• Magnesium makes up 2.1%.
• Over 90% of minerals in the Earth's crust contain oxygen and silicon.
• A compound is a substance containing atoms of two or more elements chemically combined.
• Quartz is a compound of silicon (Si) and oxygen (O).
• Galena is a compound of lead (Pb) and sulphur (S).
• Calcite is a compound of calcium (Ca), carbon (C), and oxygen (O).
• Cinnabar is a compound of mercury (Hg) and sulphur (S).
• Native elements are minerals made of only single elements.
• Gold (Au), silver (Ag), copper (Cu), Sulphur (S) and diamond (C) are native elements.

Mineral Formation

• Minerals form in several ways, often from cooling magma.
• As magma cools, atoms, molecules, and ions form compounds.
• Many minerals can form from a single magma mass, depending on its chemical composition.
• The rate of cooling determines the size of mineral grains.
• Mineral formation can be gradual or through evaporation on the surface or deep underground.
• Minerals can form through the magma process (cooling and solidification) or the metamorphic process (extreme heat and pressure).
• A mineral has a fixed chemical formula, while a rock is a mixture of minerals.
• Rocks are mixtures of minerals and come in three types: igneous, sedimentary, and metamorphic.

Mineral Structure

• The arrangement of atoms in a mineral can be seen in the shape of the mineral (crystals).
• A crystal is a regular geometric solid with smooth surfaces called crystal faces.
• Halite consists of sodium (Na) and chlorine (Cl) ions arranged in a cubic pattern.
• Each type of mineral has its own shape of crystals; quartz has a six-sided (hexagonal) crystal.
• Despite thousands of different minerals, there are only six basic types of crystal shapes.

Silicates

• Silicates are minerals containing silicon and oxygen, along with metallic elements.
• Silicates are common, making up 90% of the minerals in Earth's crust.
• Minerals are solid, with molecules, ions, and atoms closely packed.
• Increased temperature weakens a mineral's bonds, causing it to melt or vaporize; geologists use this to identify minerals

Physical Properties

• Cleavage is how a mineral splits or breaks along definite planes.
• Some minerals split easily (halite), while others have poor or no cleavage planes (quartz).
• Hardness varies due to the arrangement of atoms inside each mineral.
• Carbon can be soft in a sheet-like pattern (graphite) or hard in a pyramid-like pattern (diamond).