Asked by dom
properties of a mineral
All Answers 1
Answered by
GPT-5 mini
AI
Here are the main physical and diagnostic properties geologists use to describe and identify minerals, with short definitions, how to test them, and common examples.
1. Color
- Visual color of the specimen.
- Quick but often unreliable (many minerals have variable color due to impurities).
- Examples: sulfur = yellow; malachite = green; azurite = blue.
2. Streak
- Color of the powdered mineral (rub on unglazed porcelain streak plate).
- More reliable than surface color.
- Examples: pyrite has a black-greenish streak; hematite often reddish-brown streak.
3. Luster
- How a surface reflects light (e.g., metallic, vitreous/glassy, pearly, silky, dull).
- Examples: pyrite = metallic; quartz = vitreous; talc = pearly to greasy.
4. Hardness (Mohs scale)
- Resistance to scratching; compared against reference minerals (1–10).
- Mohs scale: 1 talc, 2 gypsum, 3 calcite, 4 fluorite, 5 apatite, 6 orthoclase feldspar, 7 quartz, 8 topaz, 9 corundum, 10 diamond.
- Test by scratching or using a set of picks.
5. Cleavage and fracture
- Cleavage: tendency to break along preferred crystallographic planes (described by number and angle of planes; e.g., perfect, good, poor).
- Fracture: breakage without cleavage (e.g., conchoidal, uneven, splintery).
- Examples: mica has perfect one-direction cleavage; calcite has three directions of cleavage; quartz fractures conchoidally.
6. Crystal form / habit
- External shape of crystals (e.g., prismatic, tabular, bladed, massive, fibrous).
- Reflects internal crystal structure (crystal system: cubic/isometric, hexagonal, tetragonal, orthorhombic, monoclinic, triclinic).
- Example: halite forms cubic crystals; quartz commonly forms hexagonal prisms.
7. Specific gravity (density)
- Mass per unit volume relative to water; measured with balance and water or specific-gravity bottle.
- Heavy minerals (high SG): galena, magnetite; light minerals: quartz, feldspar.
8. Tenacity
- Behavior when deformed: brittle, malleable, sectile, elastic, flexible.
- Examples: gold is malleable; mica is elastic/ flexible in thin sheets.
9. Magnetism
- Attraction to a magnet (simple test).
- Example: magnetite is strongly magnetic.
10. Reaction to dilute hydrochloric acid (HCl)
- Effervescence (fizz) indicates carbonate minerals (e.g., calcite strongly effervesces; dolomite reacts weakly unless powdered).
11. Taste / smell / feel
- Rarely used but diagnostic for some: halite tastes salty (don’t taste unknown minerals unless safe); sulfur smells of rotten eggs when powdered; talc feels soapy.
12. Fluorescence / phosphorescence
- Glow under UV light (short-wave or long-wave).
- Examples: fluorite fluoresces; scheelite fluoresces under short-wave UV.
13. Optical properties (thin section microscopy)
- Refractive index, birefringence, pleochroism—used in petrography to identify minerals in thin sections.
14. Radioactivity and X-ray properties
- Some minerals (uraninite, carnotite) are radioactive; X-ray diffraction gives definitive crystal structure.
Practical approach to identify a mineral
- Start with color and luster, then streak, hardness, cleavage/fracture, acid test, magnetism, and specific gravity. Use Mohs hardness kit, streak plate, hand lens, magnet, and dilute HCl if available. For ambiguous cases, XRD or chemical analysis may be required.
If you have a specific specimen or photo, tell me its observable features (color, streak, hardness test result, cleavage, reaction to acid, magnetism, etc.) and I can help narrow the ID.
1. Color
- Visual color of the specimen.
- Quick but often unreliable (many minerals have variable color due to impurities).
- Examples: sulfur = yellow; malachite = green; azurite = blue.
2. Streak
- Color of the powdered mineral (rub on unglazed porcelain streak plate).
- More reliable than surface color.
- Examples: pyrite has a black-greenish streak; hematite often reddish-brown streak.
3. Luster
- How a surface reflects light (e.g., metallic, vitreous/glassy, pearly, silky, dull).
- Examples: pyrite = metallic; quartz = vitreous; talc = pearly to greasy.
4. Hardness (Mohs scale)
- Resistance to scratching; compared against reference minerals (1–10).
- Mohs scale: 1 talc, 2 gypsum, 3 calcite, 4 fluorite, 5 apatite, 6 orthoclase feldspar, 7 quartz, 8 topaz, 9 corundum, 10 diamond.
- Test by scratching or using a set of picks.
5. Cleavage and fracture
- Cleavage: tendency to break along preferred crystallographic planes (described by number and angle of planes; e.g., perfect, good, poor).
- Fracture: breakage without cleavage (e.g., conchoidal, uneven, splintery).
- Examples: mica has perfect one-direction cleavage; calcite has three directions of cleavage; quartz fractures conchoidally.
6. Crystal form / habit
- External shape of crystals (e.g., prismatic, tabular, bladed, massive, fibrous).
- Reflects internal crystal structure (crystal system: cubic/isometric, hexagonal, tetragonal, orthorhombic, monoclinic, triclinic).
- Example: halite forms cubic crystals; quartz commonly forms hexagonal prisms.
7. Specific gravity (density)
- Mass per unit volume relative to water; measured with balance and water or specific-gravity bottle.
- Heavy minerals (high SG): galena, magnetite; light minerals: quartz, feldspar.
8. Tenacity
- Behavior when deformed: brittle, malleable, sectile, elastic, flexible.
- Examples: gold is malleable; mica is elastic/ flexible in thin sheets.
9. Magnetism
- Attraction to a magnet (simple test).
- Example: magnetite is strongly magnetic.
10. Reaction to dilute hydrochloric acid (HCl)
- Effervescence (fizz) indicates carbonate minerals (e.g., calcite strongly effervesces; dolomite reacts weakly unless powdered).
11. Taste / smell / feel
- Rarely used but diagnostic for some: halite tastes salty (don’t taste unknown minerals unless safe); sulfur smells of rotten eggs when powdered; talc feels soapy.
12. Fluorescence / phosphorescence
- Glow under UV light (short-wave or long-wave).
- Examples: fluorite fluoresces; scheelite fluoresces under short-wave UV.
13. Optical properties (thin section microscopy)
- Refractive index, birefringence, pleochroism—used in petrography to identify minerals in thin sections.
14. Radioactivity and X-ray properties
- Some minerals (uraninite, carnotite) are radioactive; X-ray diffraction gives definitive crystal structure.
Practical approach to identify a mineral
- Start with color and luster, then streak, hardness, cleavage/fracture, acid test, magnetism, and specific gravity. Use Mohs hardness kit, streak plate, hand lens, magnet, and dilute HCl if available. For ambiguous cases, XRD or chemical analysis may be required.
If you have a specific specimen or photo, tell me its observable features (color, streak, hardness test result, cleavage, reaction to acid, magnetism, etc.) and I can help narrow the ID.
Submit Your Answer
We prioritize human answers over AI answers.
If you are human, and you can answer this question, please submit your answer.