Mineral Properties
Posted on May 6, 2024 in Geology
Mineral Properties
Physical Properties
I. – Specific Gravity
- Number that expresses the relationship between weight and volume of water at 4°C.
II. – Mechanical Properties
Fracture
- Conchoidal: Surface leaves that break into a shell-like shape, smooth and soft.
- Shatter: Breaks into sliver-shaped pieces. Examples: Asbestos, Marcasite.
- Hooked: Breaks in one direction, leaving points or hooks. Examples: Native Cu, Ag, Au.
- Irregular: Uneven and irregular. Example: Tetrahedrite.
Hardness
- Mohs scale: Measures the resistance of a mineral to being scratched. Ranges from 1 (softest) to 10 (hardest).
Toughness
- Resistance to breakage by mechanical action.
- Fragile: Easily broken or reduced to powder. Examples: Blenda, Galena.
- Sectile: Can be cut into thin shavings with a knife.
- Malleable: Can be hammered into thin sheets. Examples: Graphite, Au, Ag, Cu (native).
- Ductile: Can be stretched into a thread. Examples: Au, Ag, Cu.
- Flexible: Can be deformed but does not return to its original position. Examples: Talc, Chlorite.
- Elastic: Resists displacement of its molecules and atoms. Recovers its original shape upon cessation of force. Examples: Biotite, Muscovite.
Optical Properties
1. – Optical Surface Properties
a) Gloss or Brilliance
- Depends on the nature, intensity, and reflection of light.
- Variations in light quantity produce different degrees of luster or brilliance:
- Brilliant: Produces sharp images.
- Soft: Does not produce sharp images.
- Weak: Reflects light without images.
- Matte: Does not produce reflection.
b) Color of Minerals
- Due to the combined effect of radiation absorption.
- If all wavelengths are reflected, the mineral appears white. If some wavelengths are absorbed, the mineral appears colored.
- Colors include: white, green, yellow, gray, red, blue, black, brown, and all tones in between.
c) Color of Streak
- Color of the line or powder obtained by rubbing the mineral across an unglazed porcelain plate.
d) Play of Colors
- Different colors appear when the mineral is turned in different directions.
e) Opalescence
- Pearly reflection of light from the mineral’s surface.
f) Iridescence
- Presence of different prismatic colors on the mineral’s surface.
2. – Optical Internal Properties
- When light propagates through the mineral.
a) Isotropic Minerals
- Monorefringent: Elasticity is identical in all directions.
b) Birefringent Minerals
- Elasticity is different in two directions, resulting in different refractive indices and the formation of two rays of light.
c) Phosphorescence
- Emission of light after exposure to radiation.
d) Fluorescence
- Emission of light when exposed to ultraviolet light.
Thermal Properties
- When heat is applied to minerals.
a) Fusibility
- Important for mineral identification.
- Measured using a blowpipe and a fusibility scale.
b) Thermal Conductivity
- Ability to conduct heat.
- Isotropic minerals have equal conductivity in all directions, while birefringent minerals have different conductivity in different directions.
c) Dilatation
d) Diathermancy
- Ability to transmit heat rays.
- Diathermic minerals allow heat rays to pass through, while athermanous minerals do not.
Electrical and Magnetic Properties
a) Electrical Conductivity
- Ability to conduct electricity.
b) Pyroelectricity
- Certain dielectric crystals become electrically charged when heated.
c) Piezoelectricity
- Certain crystals become electrically charged when subjected to pressure.
d) Magnetism
- Some minerals are attracted to magnets.
Organoleptic Properties
- Properties that can be detected by the senses.
a) Taste
- Astringent (sulfate taste)
- Alkaline (carbonate taste)
- Bitter (Epsom salts taste)
- Salty (common salt taste)
- Fresh (nitrate taste)
- Acidic (sulfuric acid taste)
b) Smell
- Alliaceous (garlic smell)
- Sulfurous (pyrite smell)
- Radishy (radish smell)
- Oily (bitumen smell)
- Fetid (hydrogen sulfide or rotten egg smell)
- Earthy (mud smell)
c) Touch
- Smooth (spiolite)
- Greasy (talc)
- Lean (aspro)
