Minerals and Rocks – Physical & Chemical Properties

30 Q&A flashcards summarizing definitions, properties, and classifications of minerals, plus details on the Mohs scale and diagnostic tests.

What is the geological definition of a mineral?

A naturally occurring, inorganic solid with an orderly crystalline structure and a definite chemical composition.

Why are minerals considered the basic building blocks of rocks?

Because rocks are aggregates of one or more minerals that crystallized together or were cemented together.

Which two elements make up the silicon-oxygen tetrahedron that forms the basis of all silicate minerals?

Silicon (Si) and Oxygen (O).

About what percentage of all rock-forming minerals are silicates?

More than 90 %.

What physical property measures a mineral’s resistance to abrasion?

Hardness.

Who created the Mohs scale of hardness and in what year?

Friedrich Mohs in 1812.

According to the Mohs scale, which mineral has the lowest hardness and what is its value?

Talc, hardness 1 (very soft).

Which Mohs scale mineral can scratch glass (hardness ≥6)?

Any mineral with hardness 6 or greater, e.g., Feldspar (hardness 6).

Which mineral ranks 10 (the hardest) on the Mohs scale?

Diamond.

State one advantage and one disadvantage of the Mohs scale.

Advantage: Quick, easy field test with simple tools. Disadvantage: Qualitative only; cannot measure exact hardness of industrial materials.

Define luster in mineralogy.

The quality and intensity of light reflected from a mineral’s surface.

Give two examples of non-metallic luster types.

Vitreous (glassy) and pearly (others include adamantine, resinous, silky, dull, greasy).

Why is streak often more diagnostic than color when identifying minerals?

Because streak represents the mineral’s powdered color, which is less affected by impurities than external color.

What is the streak color of pyrite and why is this important?

Black to dark gray; it distinguishes pyrite from gold despite its metallic-gold external color.

Define crystal habit (form).

The external shape a crystal or aggregate of crystals develops as it grows in open space, reflecting its internal atomic structure.

How does cleavage differ from crystal habit?

Cleavage forms after crystallization along planes of atomic weakness; habit forms during crystal growth.

Provide the definition of cleavage in minerals.

The tendency of a mineral to break along flat, parallel planes of weakness, producing smooth surfaces.

Name three common cleavage descriptions and give an example for one.

One direction (biotite), two directions at 90° (orthoclase), three directions at 74° (calcite).

What term describes irregular, non-planar breakage in minerals without cleavage?

Fracture.

Give an example of a mineral that exhibits conchoidal fracture.

Quartz.

Define specific gravity in mineral studies.

The ratio of a mineral’s weight to the weight of an equal volume of water; numerically equal to its density relative to water.

Which mineral property explains why a bucket of silver weighs ten times more than an equal-sized bucket of water?

Specific gravity (silver SG ≈10).

List three ‘other’ diagnostic properties used to identify minerals and give an example for each.

Magnetism (magnetite), odor (sulfur), reaction with acid (calcite or powdered dolomite).

What characterizes minerals in the oxide class?

They contain the oxygen anion (O²⁻) combined with one or more metal ions.

Describe minerals in the sulfate group.

They possess the sulfate anion (SO₄²⁻) combined with other ions.

Why are sulfide minerals economically important?

They often host valuable metals such as copper, lead, and zinc.

Give the chemical anion that defines carbonate minerals.

Carbonate anion (CO₃)²⁻.

What are native elements and how are they sub-grouped?

Minerals consisting of a single element; subdivided into metals/inter-metals (e.g., gold), semi-metals (arsenic), and non-metals (sulfur, diamond).

Which mineral class contains halogen elements bonded to one or more other elements?

Halides.

State the learning competency for this lesson as specified in the curriculum guide.

Learners should be able to identify common rock-forming minerals using their physical and chemical properties (S11ES-Ib-5).