Geologists classify minerals based on a set of specific characteristics, which are collectively referred to as mineral properties. These properties help to identify and distinguish different minerals from one another. Here are the key characteristics:

1. Chemical Composition:

* Elements: Minerals are composed of specific elements arranged in a definite ratio. This is the most fundamental property used for classification. For example, quartz is always made of silicon and oxygen in a 1:2 ratio (SiO2).

* Chemical Formula: A chemical formula represents the elements and their proportions within a mineral. For example, the formula for halite (table salt) is NaCl.

2. Crystal Structure:

* Internal Arrangement: Atoms in a mineral are arranged in a specific, repeating pattern called a crystal lattice. This structure determines the mineral's shape, cleavage, and other properties.

* Crystal System: Minerals are further categorized based on their crystal system, which refers to the symmetry and arrangement of their crystal lattice. There are seven crystal systems: cubic, tetragonal, hexagonal, orthorhombic, monoclinic, triclinic, and rhombohedral.

3. Physical Properties:

* Hardness: The resistance of a mineral to scratching, measured on Mohs Hardness Scale. Diamond is the hardest mineral (10), while talc is the softest (1).

* Cleavage: The tendency of a mineral to break along specific planes of weakness in its crystal structure. This results in smooth, flat surfaces.

* Fracture: How a mineral breaks when it doesn't cleave. This can be conchoidal (shell-like), splintery, or uneven.

* Luster: How light reflects off the surface of a mineral, described as metallic, glassy, pearly, etc.

* Color: While color can be variable, some minerals have characteristic colors that help with identification.

* Streak: The color of the mineral's powder when rubbed against a streak plate.

* Specific Gravity: The ratio of a mineral's density to the density of water.

* Magnetism: Some minerals are magnetic, like magnetite.

* Fluorescence: Some minerals glow under ultraviolet light.

4. Other Properties:

* Taste: Halite (table salt) is the only common mineral with a salty taste.

* Smell: Some minerals have a distinct smell, like sulfur.

* Feel: Some minerals feel greasy (talc), smooth (calcite), or rough (quartz).

It's important to note:

* Multiple properties are usually used to identify a mineral, not just one.

* Some properties, like color, can be variable and misleading.

* Geologists use a combination of these properties, alongside laboratory tests, to accurately classify minerals.