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 b. Seawater c. Quartz d. Cubic zirconia e. Obsidian f. Ruby g. Glacial ice h. Amber Refer to the periodic table of the elements (Figure 3.5 ) to help answer Questions 2 and 3 .

Short answer

Minerals: Gold nugget, Quartz, Ruby, Glacial ice. Non-minerals: Seawater, Cubic zirconia, Obsidian, Amber.

Step-by-step solution

Understand the Definition of a Mineral

A mineral is defined as a naturally occurring, inorganic solid with a definite chemical composition and an ordered atomic structure. The key characteristics of a mineral are: it must be naturally occurring, solid, inorganic, have a fixed chemical formula, and a crystalline structure.

Evaluate Gold Nugget

Gold nuggets are naturally occurring substances made of the element gold. They have a definite chemical composition (Au) and crystalline structure. Thus, a gold nugget is a mineral.

Evaluate Seawater

Seawater is a liquid and not a solid. Although it contains minerals dissolved within, seawater itself cannot be classified as a mineral due to its liquid state.

Evaluate Quartz

Quartz is a naturally occurring mineral composed of silicon dioxide (SiO2) with a defined crystalline structure. Therefore, quartz is classified as a mineral.

Evaluate Cubic Zirconia

Cubic zirconia is a synthetic material, meaning it is not naturally occurring. As minerals must be naturally occurring, cubic zirconia is not a mineral.

Evaluate Obsidian

Obsidian is a volcanic glass, which is an amorphous (non-crystalline) solid. Because minerals must have a crystalline structure, obsidian is not a mineral.

Evaluate Ruby

Ruby is a naturally occurring mineral composed primarily of aluminum oxide (Al2O3) with trace elements that give it color. It has a crystalline structure, so ruby is a mineral.

Evaluate Glacial Ice

Glacial ice is naturally occurring and has a crystalline structure (solid water with fixed H2O composition). It is considered a mineral.

Evaluate Amber

Amber is fossilized tree resin. It is organic in nature, which disqualifies it from being a mineral, as minerals must be inorganic.

Key concepts

Minerals

Minerals are fascinating substances that form the building blocks of rocks. In geology, a mineral is defined by several key features. Firstly, it must be naturally occurring, meaning it forms through natural processes rather than being man-made.
Secondly, a mineral is an inorganic material, which means it is not derived from living organisms. Additionally, minerals are solid, so anything liquid or gas does not fit within this definition.
Another important aspect of minerals is their definite chemical composition. This means each mineral type has a specific chemical formula that remains consistent regardless of where it is found. Lastly, minerals have an ordered atomic structure, often forming a crystalline structure, which gives them their unique geometric shapes.

Chemical Composition

The chemical composition of a mineral is like its fingerprint, dictating its properties and classification. Each mineral has a specific chemical formula that remains the same throughout different samples.
For example, the mineral quartz has the chemical formula SiO₂, indicating it is composed of silicon and oxygen in a 1:2 ratio. This precise composition is crucial, as even slight variations define different minerals.
Understanding a mineral’s chemical makeup helps geologists determine its identity and its potential uses. When different elements combine in fixed proportions, they create a unique composition that characterizes the mineral, helping in scientific and practical applications.

Crystalline Structure

Crystalline structure refers to the orderly, repeating arrangement of atoms within a mineral. This internal structure is responsible for many physical properties of minerals, including hardness, cleavage, and crystal shape.
Minerals with a crystalline structure have their atoms or ions arranged in a regular and repeating pattern, which often results in beautiful and varied external forms. This arrangement is not random but follows geometric principles, leading to the unique shapes observed in crystals.
For instance, a ruby, primarily made up of aluminum oxide, has a well-defined crystalline structure that contributes to its hardness and vivid color. Crystals can grow in numerous forms depending on the space and conditions available during their formation.

Natural Occurrence

For a substance to be considered a mineral, it must occur naturally within the Earth. This natural occurrence aspect means humans cannot synthesize true minerals in laboratories or factories.
Substances such as gold nuggets and glacial ice meet this criterion as they are formed by natural processes without human intervention. However, man-made items like cubic zirconia do not qualify as minerals due to this requirement.
The origin story of minerals often involves geological processes like cooling lava, precipitating from solutions, or performing sedimentary and metamorphic transformations. Each process contributes to the vast diversity of minerals found in nature, attracting geologists and enthusiasts alike to study and admire them.