Mineral Properties and the Complete Rock Cycle Explained

Posted on Dec 24, 2025 in Geology

Mineral Properties and Formation

Origin of Minerals

The origin of minerals can be:

  • Within a mass of molten rock (magma), such as feldspar or olivine.
  • Within solid rocks under high pressures and temperatures, such as calcite.

Properties of Minerals

Color
The type of light a mineral reflects when illuminated.
Luster (Brightness)
The way a mineral reflects light (e.g., metallic, glassy, dull).
Hardness
The resistance of a mineral to being scratched.
Streak (Color of the Line)
The color of the dust that occurs when a mineral is scratched against a streak plate.
Cleavage (Peel)
The property of a mineral breaking into fragments that retain flat faces.

Mohs Scale of Hardness

The hardness of minerals is expressed by a number referred to a scale of ten reference minerals called the Mohs Scale. Each mineral scratches all those that have a lower number and is scratched by those that have an equal or greater number.

Classification of Key Minerals

  • Silicates: Quartz, Orthoclase, Andalusite, Mica, Garnet, Kaolin, Talc.
  • Iron Group: Pyrite, Magnetite, Siderite, Hematite (Oligisto), Limonite.
  • Copper Group: Cuprite, Malachite, Azurite, Native Copper, Chalcopyrite.
  • Zinc Group: Sphalerite (Zinc Blende).
  • Aluminum Group: Bauxite, Corundum.
  • Lead Group: Galena.
  • Tin Group: Cassiterite.
  • Uranium Group: Wolframite, Uraninite.
  • Mercury Group: Native Mercury, Cinnabar.

Other Important Minerals

Filonianos, Liquid Gold, Silver, Platinum, Diamond, Graphite, Fluorite, Calcite, Iceland Spar.

Metamorphism of Sedimentary Rocks

Accumulations push the rocks, which at great depths are subjected to high pressures and temperatures. This causes metamorphism.

Formation of Rocks: The Rock Cycle

Rocks are formed through several processes:

  1. Cooling of magma.
  2. Disintegration, transport, and deposition of existing rock material.
  3. Precipitation of inorganic salts dissolved in water.
  4. Condensation of gases containing mineral particles, animal remains, and plant remains.
  5. Partial or complete recrystallization of minerals in a rock due to high temperatures and pressure.

Igneous Rock Formation

By crystallization of magma, igneous rocks are formed. These may be classified as basic, acidic, or intermediate depending on their composition. They are also classified as plutonic (intrusive) or volcanic (extrusive), depending on whether consolidation occurred within the Earth or on its surface.

Sedimentary Rock Formation

Consolidated igneous rocks, subjected to weathering, fragment or disintegrate into smaller particles or clasts to form sediments. These sediments are then transported and accumulated in a proper basin, where they undergo a process of hardening or compaction called diagenesis or lithification, thereby forming sedimentary rocks.

Sedimentary rocks are formed by layers of different grain sizes. Through lithification:

  • Sands become sandstones.
  • Silts become shales.
  • Calcareous material becomes limestone.
  • Gravels become conglomerates.

Metamorphism and Metamorphic Rocks

Sedimentary and igneous rocks can undergo the action of high temperatures and high pressures caused by various factors, leading to marked textural and mineralogical changes. This process, which does not require passage through the liquid state, is called metamorphism, and the resulting rocks are metamorphic rocks.

The Complete Rock Cycle

Finally, igneous, sedimentary, and metamorphic rocks, under the action of strong pressures and high temperatures with special conditions, can undergo melting or remelting to return to the primitive magmatic state, thus beginning a new cycle.