Question

Using the geologic definition of mineral as your guide, determine which of the items on the list are minerals and which are not. If not a mineral, explain. a. gold nugget b. sea water c. quartz d. cubic zirconia e. obsidian f. ruby g. glacial ice h. amber

Short answer

Minerals: gold nugget, quartz, ruby, glacial ice. Not minerals: sea water, cubic zirconia, obsidian, amber.

Step-by-step solution

Define Mineral

A mineral, according to geology, must meet the following criteria: it is a naturally occurring, inorganic solid, has a defined chemical composition, and possesses a crystalline structure.

Evaluate Gold Nugget

A gold nugget is naturally occurring, inorganic, has a fixed chemical composition made of gold (Au), and is crystalline in structure. Thus, a gold nugget is a mineral.

Evaluate Sea Water

Sea water is naturally occurring and inorganic but is a liquid, not a solid, and does not have a fixed chemical composition. Therefore, sea water is not a mineral.

Evaluate Quartz

Quartz is naturally occurring, inorganic, solid, has the chemical composition SiO₂, and a crystalline structure. Therefore, quartz is a mineral.

Evaluate Cubic Zirconia

Cubic zirconia is not naturally occurring as it is manufactured. Despite being inorganic and solid, it does not meet all criteria for being a mineral. Hence, it is not a mineral.

Evaluate Obsidian

Obsidian is naturally occurring and is a solid, but it is volcanic glass with no crystalline structure. Hence, it does not qualify as a mineral.

Evaluate Ruby

Ruby is a variety of the mineral corundum. It is naturally occurring, inorganic, solid, has a definite chemical composition (Al₂O₃), and crystalline structure. Thus, ruby is a mineral.

Evaluate Glacial Ice

Glacial ice is naturally occurring, inorganic, has a defined structure, and when solid, has a crystalline structure. Therefore, glacial ice is classified as a mineral.

Evaluate Amber

Amber is a solid, but it is organic as it is formed from the resin of trees and does not have a crystalline structure. Therefore, amber is not a mineral.

Key concepts

Geology

Geology is the scientific study of Earth, including its composition, structure, and processes that shape it. When it comes to minerals, geologists play a crucial role in identifying and classifying them based on specific criteria. A mineral must be naturally occurring, meaning it forms without human intervention. It should also be an inorganic solid, have a definite chemical composition, and possess a specific crystalline structure. These criteria help geologists determine whether a substance like quartz or gold qualifies as a mineral. By understanding these principles, students can better analyze geological samples and appreciate the Earth's natural resources.

Crystalline Structure

The crystalline structure of a mineral refers to how its atoms are organized in a repeating, three-dimensional pattern. This orderly arrangement contributes to the unique shape, or crystal form, of mineral specimens. For example, quartz features a hexagonal crystal system, which means its atoms are arranged in a repeating pattern that reflects its chemical composition of silicon dioxide (SiO₂).
Crystalline structure is a key characteristic in mineral classification because it influences many of the mineral's physical properties, including cleavage, hardness, and optical properties. Without a crystalline structure, as in the case of obsidian, a substance cannot be classified as a mineral.

Inorganic Solid

To qualify as a mineral, a substance must be an inorganic solid. This means it cannot originate from living organisms. Inorganic solids are formed through natural geologic processes such as cooling lava or crystallizing from a solution. They hold a solid state, which is crucial because it allows them to maintain a crystalline structure. Examples include minerals like quartz and ruby, whereas substances such as amber, derived from organic tree resin, do not qualify as they do not meet this criterion.

• The distinction between organic and inorganic is important for proper mineral classification.
• Only inorganic solids should be considered when determining if a substance meets the mineral criteria.

Understanding this helps in evaluating natural samples accurately.

Chemical Composition

Chemical composition is essential when defining a mineral, as it provides a mineral with its identity. Minerals possess a specific chemical formula that denotes the types and proportions of elements within them. For instance, the mineral quartz is composed of silicon and oxygen, represented as SiO₂.
This uniformity in chemical composition contributes to the predictability of a mineral's properties. For example, the consistent chemical structure of quartz ensures its hardness and resistance to weathering. In contrast, sea water lacks a defined chemical composition; it contains a mixture of salt, water, and other dissolved substances, making it ineligible for mineral classification. Consistent and specific chemical composition is what sets true minerals apart from other naturally occurring substances.