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 an item is not a mineral, explain why not. a. gold nugget b. seawater c. quartz d. cubic zirconia e. obsidian f. ruby g. glacial ice h. amber

Short answer

Gold, quartz, ruby, and glacial ice are minerals; seawater, cubic zirconia, obsidian, and amber are not.

Step-by-step solution

- Understanding the Mineral Definition

A mineral is a naturally occurring, inorganic solid with a definite chemical composition and an ordered atomic structure. This means that to be classified as a mineral, a substance must be natural, solid, inorganic, have a specific chemical formula, and have a crystal structure.

- Analyzing the Gold Nugget

Gold is a naturally occurring, inorganic solid with a definite chemical composition and an ordered atomic structure. Therefore, a gold nugget is classified as a mineral.

- Investigating Seawater

Seawater is a liquid and not a solid. Although it contains minerals dissolved within it, seawater itself does not meet the criterion of being a naturally occurring solid. Therefore, seawater is not a mineral.

- Examining Quartz

Quartz is a naturally occurring, inorganic solid with the chemical formula $Si{O}_2$ and a specific crystal structure. Therefore, quartz is classified as a mineral.

- Considering Cubic Zirconia

Cubic zirconia is a synthetic product made in laboratories. Although it is solid and has a specific chemical composition and crystal structure, it is not naturally occurring. Therefore, cubic zirconia is not a mineral.

- Evaluating Obsidian

Obsidian is a naturally occurring glass from volcanic origins. It lacks a specific crystal structure, being an amorphous substance. Thus, obsidian does not qualify as a mineral.

- Reviewing Ruby

Ruby is a variety of the mineral corundum, with the chemical composition $A{l}_2{O}_3$ and having a crystal structure. It is a naturally occurring, inorganic solid, so ruby is classified as a mineral.

- Assessing Glacial Ice

Glacial ice is naturally occurring, inorganic, solid, and has a crystalline structure, making it meet all the criteria for a mineral. Therefore, glacial ice is considered a mineral.

- Evaluating Amber

Amber is a naturally occurring organic compound derived from the fossilized resin of trees, lacking a definite crystal structure. Being organic, amber does not meet the criteria for minerals and is therefore not a mineral.

Key concepts

Geologic Definition of Mineral

The geologic definition of a mineral forms the foundation for understanding what qualifies as a mineral. For a substance to be classified as a mineral, it must meet five specific criteria. First, it must be **naturally occurring**, meaning it forms through natural processes without human intervention.
Secondly, a mineral must be an **inorganic solid**, which means it cannot be composed of materials that stem from living organisms. It also must be in a solid state at standard temperature and pressure.
A mineral must have a **definite chemical composition**, representing a specific chemical formula that determines what elements are present and in what proportion.
Lastly, it must have an **ordered atomic structure**, often resulting in a crystalline form. This structured arrangement of atoms gives minerals their unique internal geometries and external crystal shapes.
Understanding these characteristics is essential in mineral identification and differentiates minerals from other natural substances.

Natural vs Synthetic Substances

Understanding the difference between natural and synthetic substances is crucial in the context of minerals. **Natural substances** are those formed by geological processes without human involvement. They are created over time through various processes, such as cooling of magma or metamorphism.
In contrast, **synthetic substances** are human-made and created in laboratories or industrial processes. Even though synthetic substances might mimic the appearance and properties of natural minerals, they do not meet the criteria to be classified as true minerals due to their artificial origin.
An example from the original exercise is cubic zirconia, a widely used synthetic gemstone. While it exhibits similar physical properties to natural gemstones, it does not develop via natural processes and thus is not recognized as a mineral.

• Natural substances form naturally.
• Synthetic substances are artificially created.

In mineral identification, always consider the origin process to determine if a substance is natural or synthetic.

Crystal Structure

The crystal structure of a mineral is a key feature that significantly contributes to its identification and classification. A crystal structure refers to the unique arrangement of atoms in a mineral. This ordered atomic structure translates into a symmetrical, repeating pattern which manifests as the mineral's external geometric shape.
The symmetry in a mineral's crystal structure affects several of its properties, including its cleavage, fracture, and optical characteristics.
For example, quartz and ruby, both considered minerals, have distinct and specific atomic arrangements that result in exceptional crystal symmetry and consistent internal structures.

• Crystal structures are unique atomic arrangements.
• They define the shape and properties of minerals.

Some substances, like obsidian, do not have a crystal structure, due to their amorphous nature, and therefore cannot be classified as minerals despite being naturally occurring.
Recognizing and understanding crystal structures is essential for differentiating true minerals from other similar substances.

Inorganic Compounds

Minerals must be composed of **inorganic compounds**, meaning they are not derived from living organisms or biological processes. An inorganic compound is typically defined by its composition, lacking carbon-hydrogen bonds found in organic compounds.
This distinction is vital in the identification of minerals. For instance, amber is derived from organic resin and does not qualify as a mineral due to its organic nature. This highlights the importance of excluding organic components when determining mineral status.

• Minerals are composed of inorganic compounds.
• Organic-derived substances, like amber, are not minerals.

The inorganic criterion ensures that minerals are stable solids with consistent compositions and long-term geologic occurrence. This strictly inorganic nature allows minerals to maintain durability and structural integrity, essential qualities for various scientific and industrial applications.