Chapter 3 Flashcards
Minerals
What is a mineral, as geologists understand the term? How is this definition different from the everyday usage of the word?
A mineral is a naturally occurring, inorganic solid with a defined chemical composition and crystalline structure. In everyday use, “mineral” can refer to any valuable substance found in the ground, including non-crystalline materials like coal or water.
Why is glass not a mineral?
Glass lacks a crystalline structure; it is an amorphous solid. Minerals must have a structured, repeating atomic arrangement, which glass does not.
Salt is a mineral, but the plastic in an inexpensive pen is not. Why?
Salt is naturally occurring and has a defined chemical composition and crystalline structure, while plastic is synthetic, lacks a crystalline structure, and doesn’t occur naturally.
Describe several ways that mineral crystals can form.
Mineral crystals can form through solidification of a melt, precipitation from a solution, solid-state diffusion, biomineralization, and fumarolic mineralization
Why do some minerals occur as euhedral crystals, whereas others occur as anhedral grains?
Euhedral crystals form with well-defined faces in open spaces where growth is unrestricted, while anhedral grains develop in confined spaces where crystal growth is restricted by surrounding materials.
List and define the principal physical properties used to identify a mineral. Which minerals react with acid to produce CO₂?
Key properties include color, streak, luster, hardness, specific gravity, cleavage, fracture, and crystal habit. Carbonate minerals, like calcite, react with acid to produce CO₂.
How can you determine the hardness of a mineral? What is the Mohs hardness scale?
Mineral hardness is determined by scratching it with a material of known hardness. The Mohs hardness scale ranks minerals from 1 (softest) to 10 (hardest).
How do you distinguish cleavage surfaces from crystal faces on a mineral? How does each type of surface form?
Cleavage surfaces form along planes of weakness within a mineral and are parallel to atomic layers. Crystal faces are external surfaces that form during crystal growth and reflect the mineral’s internal structure.
What is the prime characteristic that geologists use to separate minerals into classes?
Minerals are classified based on their anionic group (e.g., silicates, carbonates, oxides).
What is a silicon-oxygen tetrahedron? What is the anionic group that occurs in carbonate minerals?
The silicon-oxygen tetrahedron is a molecular structure with one silicon atom surrounded by four oxygen atoms, common in silicates. The carbonate group (CO₃²⁻) is the anionic group in carbonate minerals.
On what basis do mineralogists organize silicate minerals into distinct groups?
Silicate minerals are grouped based on the arrangement of silicon-oxygen tetrahedra, such as isolated, single chains, double chains, sheets, and frameworks.
What is the relationship between the silicon-oxygen tetrahedra bonding in micas and their characteristic cleavage?
In micas, silicon-oxygen tetrahedra are arranged in sheets. This sheet structure results in one-directional cleavage, allowing mica to split easily along flat planes.
Why are some minerals considered gemstones? How do you make the facets on a gem?
Minerals are considered gemstones if they are rare, durable, and aesthetically pleasing. Facets are made by cutting and polishing the gem at specific angles to enhance its brilliance.
Compare the chemical formula of magnetite with that of biotite. Which mineral has greater specific gravity?
Magnetite (Fe₃O₄) has a higher specific gravity due to its high iron content, compared to biotite (K(Mg,Fe)₃AlSi₃O₁₀(OH)₂), which contains less iron.
How can you determine whether a milky white crystal is plagioclase or quartz?
Plagioclase typically shows striations on its cleavage planes, whereas quartz does not. Additionally, quartz has conchoidal fracture, while plagioclase exhibits cleavage.
