Question

Using the geologic definition of mineral as your guide, determine which of the items on this list are minerals and which are not. If not a mineral, explain. a. Gold nugget e. Obsidian b. Seawater f. Ruby c. Quartz g. Glacial ice d. Cubic zirconia h. Amber

Short answer

Minerals: Gold nugget, Quartz, Ruby, Glacial ice. Not minerals: Seawater, Obsidian, Cubic zirconia, Amber.

Step-by-step solution

Definition of a Mineral

A mineral is a naturally occurring, inorganic solid with a definite chemical composition and an ordered atomic structure. It must be found in nature and must have a crystalline form.

Evaluate Gold Nugget

Gold nugget is naturally occurring and solid; it is composed of a single element, gold, and has a crystalline structure. Therefore, it is a mineral.

Evaluate Seawater

Seawater is not a solid; it is a liquid. Since one of the criteria for a mineral is that it must be solid, seawater is not a mineral.

Evaluate Quartz

Quartz is a naturally occurring mineral composed of silicon dioxide (SiO₂) with a crystalline structure. It meets all the criteria of a mineral, so it is a mineral.

Evaluate Cubic Zirconia

Cubic zirconia is synthetic and man-made, meaning it is not naturally occurring. Therefore, it is not a mineral by geologic standards.

Evaluate Obsidian

Obsidian is naturally occurring and solid but lacks a definite crystalline structure as it is industrial glass. Therefore, it does not meet the criteria of a mineral.

Evaluate Ruby

Ruby is a naturally occurring, solid crystalline form of corundum (aluminum oxide) with trace chromium. It meets all criteria for being classified as a mineral.

Evaluate Glacial Ice

Glacial ice is a naturally occurring, solid form of water (H₂O) and has a crystalline structure. Consequently, it is considered a mineral.

Evaluate Amber

Amber is organic as it is derived from tree resin. Since minerals must be inorganic, amber does not qualify as a mineral.

Key concepts

Geologic Definition of Mineral

A geologic definition of a mineral helps in understanding what sets minerals apart from other substances. To classify a substance as a mineral, several characteristics must be met. Firstly, it must be naturally occurring, which means it forms through natural geological processes. Secondly, it should be inorganic, indicating it is not living or formed from living organisms.
Additionally, a mineral needs to be solid, excluding liquids and gases from being considered minerals. Having a specific chemical composition is also important, meaning the mineral must consist of a specific set of chemical elements in a defined proportion. Finally, a mineral must have an ordered atomic structure or crystalline form. This structure results in a solid where atoms are arranged in a specific, repeating pattern.
These characteristics distinguish minerals from other naturally occurring substances, making them a fundamental part of Earth's geology.

Criteria for Minerals

To determine whether a substance is a mineral, certain criteria must be evaluated. Here is a concise breakdown:

• **Naturally Occurring**: The substance must form through natural processes without human intervention.
• **Inorganic**: It should not be composed of or produced by organic life forms.
• **Solid State**: Only substances in a solid state at room temperature are considered minerals.
• **Definite Chemical Composition**: A mineral must have a specific and consistent chemical formula.
• **Ordered Atomic Structure**: The atoms within a mineral must be arranged in a repetitive crystal lattice.

Assessing if a substance meets all these criteria is essential for classification as a mineral. Understanding these criteria allows geologists and students alike to distinguish between minerals and non-minerals in nature.

Mineral Identification

Mineral identification involves determining whether a substance meets all the criteria mentioned above. This process often includes examining physical and chemical properties. Some common properties that are evaluated include:

• **Color**: Detection of the mineral's overall appearance, although color can sometimes vary within the same mineral type.
• **Hardness**: Measured using the Mohs hardness scale, comparing the ability of one mineral to scratch another.
• **Luster**: Describes how a mineral reflects light, ranging from metallic to dull.
• **Streak**: The color of the powdered mineral, often observed by rubbing it on a porcelain plate.
• **Cleavage and Fracture**: The pattern in which a mineral breaks along planes or in an irregular manner.

Utilizing these properties helps to effectively and accurately identify minerals. Doing so is crucial in various fields such as geology, archeology, and environmental science, where mineral identification plays an indispensable role.

Naturally Occurring Solids

Naturally occurring solids encompass a variety of substances that form without human intervention. These include both minerals and non-crystalline solids. While all minerals are naturally occurring solids, not all naturally occurring solids qualify as minerals.
For instance, substances like volcanic glass, known as obsidian, are formed naturally but lack a crystalline structure due to rapid cooling processes. As a result, they do not meet all the criteria for being minerals. Similarly, substances like amber, though solid and natural, are organic and hence not minerals.
Naturally occurring solids can provide a wealth of information about Earth's history and geological processes. They participate in shaping the planet's surface and are crucial for understanding natural processes and ecosystems.