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To understand what qualifies as a mineral, it's important to know the specific criteria that must be met. In geology, a mineral is defined by five characteristics:

• **Naturally Occurring**: The substance must form through natural geological processes.
• **Inorganic**: It must not be derived from living organisms. If something originates from biological processes, it doesn't fit as a mineral.
• **Solid**: Minerals must possess a solid state at room temperature. Liquids and gases are excluded.
• **Definite Chemical Composition**: Each mineral has a specific chemical formula and consistent elemental makeup.
• **Ordered Internal Structure**: A true mineral exhibits a crystalline structure, meaning its atoms are arranged in an organized, repeating pattern.

When evaluating substances like quartz or ruby, each fulfills the criteria: they are naturally occurring, inorganic solids, with definitive chemical compositions and ordered structures. Conversely, substances like amber, with organic origins, and seawater, in liquid form, fail to meet these mineral requirements.

The classification of minerals is a vast and rich field within geology. It involves organizing minerals based on their chemical composition and crystal structure.

• **Chemical Composition**: Minerals are primarily classified according to their dominant chemical component, such as silicates, carbonates, oxides, and sulfides.
• **Crystal Structure**: The way atoms are stacked in a mineral contributes to its classification. For instance, while graphite and diamond are both forms of carbon, their differing atomic arrangements give them distinct properties.

This classification helps geologists identify minerals in the field and understand their role in the Earth's crust. Minerals like quartz fall into the silicate category due to their silicate (SiO2) makeup, while ruby, a variety of corundum, is classified as an oxide due to its composition (Al2O3). By knowing a substance's classification, we can gain insights into how it formed and its potential uses and properties.

The geological definition of a mineral is precise, focusing on the characteristics and formation processes that set minerals apart from other substances.
A geological mineral is a substance that is naturally formed, meaning it originates in the Earth without human intervention. It must be inorganic, which excludes any material that is a product of life processes.

• **Essential Characteristics**: These include being solid with a stable shape and structure and having a specific chemical composition that does not change over time.
• **Formative Processes**: Minerals primarily form through geological processes such as cooling of molten rock, evaporation, and pressure-induced crystallization.

Understanding minerals' geological definition helps predict their presence in particular rock formations and environmental conditions, making them crucial to studying Earth's geology. For example, glacial ice is considered a mineral because it fits all these geological criteria despite being water in solid form (H2O), indicating its capacity to form through natural processes like freezing.