Question

Using the geologic definition of mineral as your guide, determine which of the items in this list are minerals and which are not. If something in this list is not a mineral, explain. a. Gold nugget d. Cubic zirconia g. Glacial ice b. Seawater e. Obsidian h. Amber c. Quartz f. Ruby Refer to the periodic table of the elements (see Figure 2.5 ) to help you answer Questions 2 and 3 .

Short answer

Minerals: Gold, Quartz, Ruby, Glacial Ice. Not minerals: Seawater, Cubic Zirconia, Obsidian, Amber (due to not meeting one or more mineral criteria).

Step-by-step solution

Understand the Definition of a Mineral

According to geologic terms, a mineral must meet five specific criteria: it must be naturally occurring, inorganic, solid, have a definite chemical composition, and an ordered internal structure.

Evaluate Gold Nugget

A gold nugget is naturally occurring, inorganic, solid, has a definite chemical composition (Au), and an ordered atomic structure. Hence, it is a mineral.

Evaluate Seawater

Seawater is not considered a mineral because, although it contains minerals, it is a liquid rather than a solid.

Evaluate Quartz

Quartz is naturally occurring, solid, inorganic, has a definite chemical composition (SiO2), and a crystalline structure. Therefore, it is a mineral.

Evaluate Cubic Zirconia

Cubic zirconia is synthetic and not naturally occurring, although it is solid, has a chemical composition, and a crystalline structure. Thus, it is not a mineral.

Evaluate Obsidian

Obsidian is a glass formed from volcanic lava and is naturally occurring and solid. However, it lacks a crystalline structure, so it is not considered a mineral.

Evaluate Ruby

Ruby is naturally occurring, has a crystalline structure, is inorganic, solid, and has a definite chemical composition (a variety of corundum, Al2O3, with trace Cr). Therefore, it is a mineral.

Evaluate Glacial Ice

Glacial ice is naturally occurring, solid, inorganic, has a definite chemical composition (H2O), and a crystalline structure. Thus, it is considered a mineral.

Evaluate Amber

Amber is derived from the fossilized resin of ancient trees. Although solid and naturally occurring, it is organic (derived from living organisms), so it is not classified as a mineral.

Key concepts

Mineral Criteria

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.

Mineral Classification

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.

Geological Definition of Mineral

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.