Mineral Physical Properties

Physical Properties of Minerals

• Hardness refers to a mineral's resistance to scratching.
• Color is typically the first and most easily observed property.
• Minerals have color as a result of certain wavelengths of incident light being absorbed.
• Cleavage allows minerals to break smoothly along specific internal planes.
• Fracture is the property of breaking in a more random pattern without smooth planar surfaces.
• Luster describes how a mineral's surface reflects light, and the interior reflects or refracts light.
• Streak is the color of a mineral in powder form.
• Density is the ratio of a mineral's mass to its volume.
• Crystal form refers to the geometric shape of mineral crystals.
• Magnetism most often occurs when there is an imbalance in the structural arrangement of iron ions.
• Transparency is the degree to which light is transmitted through a mineral.
• Opacity refers to the property of a substance or object to block light.
• Specific gravity is the ratio of a mineral's mass to the mass of an equal volume of water.
• Tenacity refers to a mineral's resistance to breaking.
• Most minerals don't have a taste or odor, however, some do have a distinctive taste.

The Mohs Mineral Hardness Scale

• The Mohs Hardness Scale was introduced by German Geologist Friedrich Mohs in 1812.
• The scale is based on the ability of one mineral to scratch another.
• If a mineral scratches another, it is ranked higher on the scale.
• The scale is a relative ranking, with no fixed hardness difference between numbers on the scale.

Factors Influencing Color

• The presence of an element essential to its composition
• The presence of a minor chemical impurity
• Physical defects in the crystal structure
• The mechanical mixture of very fine impurities
• The presence of finely-spaced structures in the minerals

Rock-Forming Minerals

• Out of more than 4000 minerals, a small group makes up almost 90% of the Earth's crust.
• To be considered a common rock-forming mineral, it must be one of the most abundant minerals in the Earth's crust.
• To be considered a common rock-forming mineral, it must be one of the original minerals present at the time of a crustal rock's formation.
• To be considered a common rock-forming mineral, it must be an important mineral in determining a rock's classification.

Quartz

• Quartz is one of the most abundant minerals on Earth.
• It is a crystalline form of silicon dioxide (SiO2).
• It is found in diverse colors and forms.
• Quartz can be crystalline, with visible crystals, or cryptocrystalline, with microscopic crystals.

Quartz Properties

• Color: Colorless
• Luster: Vitreous (glassy)
• Hardness: 7 on the Mohs scale
• Specific gravity: Approximately 2.65g/cm³
• Cleavage: Indistinct
• Crystal shape: Trigonal

Feldspar

• Feldspar is a large group of rock-forming minerals.
• Feldspar makes up approximately 60% of the Earth's crust.
• Feldspar is a tectosilicate.
• Its structure is a three-dimensional network of silicon and oxygen atoms.

Feldspar Properties

• Color: Highly variable; common colors include white, pink, gray, and brown; trace elements and inclusions can cause other colors.
• Luster: Vitreous (glassy)
• Hardness: 6-6.5 on the Mohs scale
• Specific gravity: Approximately 2.5-2.7g/cm³
• Cleavage: Excellent in two or three directions
• Crystal shape: Monoclinic or triclinic

Augite

• Augite is a common, dark-colored mineral that forms igneous and metamorphic rocks.
• It is a member of the pyroxene group of silicate minerals.

Augite Properties

• Color: Dark green to black
• Luster: Vitreous or shiny
• Hardness: 5.0-6.0 on the Mohs scale
• Specific gravity: 3.2-3.4
• Cleavage: Imperfect, at 87° and 93°
• Crystal shape: Monoclinic and prismatic, often thick and tabular

Hornblende

• Hornblende is a dark-colored mineral that is a common component of igneous and metamorphic rocks
• It is a type of amphibole, a group of silicate minerals.

Hornblende Properties

• Color: Dark green to black
• Crystal structure: Monoclinic
• Cleavage: Present at 56° and 124°, creating a diamond shape in cross-section
• Minor elements: Often contains manganese, titanium, chromium, potassium, fluorine, and yttrium