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name: mineral-identification locale: caveman-lite source_locale: en source_commit: 82c77053 fence_basis_commit: 82c77053 translator: "Julius Brussee homage — caveman" translation_date: "2026-04-26" description: > Field identification of minerals and ores using hardness, streak, luster, cleavage, crystal habit, and simple chemical tests. Covers systematic elimination, Mohs scale application, and common ore indicators for precious metals, gemstones, and industrial minerals. Use when encountering an unknown rock or mineral specimen, when prospecting and assessing whether a site shows valuable mineral indicators, when distinguishing ore-bearing rock from barren rock, or when building geological literacy through observation. license: MIT allowed-tools: Read metadata: author: Philipp Thoss version: "1.0" domain: prospecting complexity: intermediate language: natural tags: prospecting, minerals, geology, identification, hardness, streak, field-geology

Mineral Identification

Identify minerals in the field using physical properties, systematic elimination, and field tests.

When to Use

• You find an unknown rock or mineral specimen and want to identify it
• You are prospecting and need to assess whether a site shows valuable mineral indicators
• You want to distinguish ore-bearing rock from barren rock in the field
• You are building geological literacy through systematic observation

Inputs

• Required: A mineral specimen or outcrop to examine
• Optional: Streak plate (unglazed porcelain tile or bathroom tile back)
• Optional: Steel nail or knife blade (hardness ~5.5)
• Optional: Glass plate (hardness ~5.5)
• Optional: Copper coin (hardness ~3.5)
• Optional: Hand lens (10x)
• Optional: Dilute hydrochloric acid (10% HCl) for carbonate test

Procedure

Step 1: Observe Without Touching

Before handling, observe the specimen in context.

Field Context:
+--------------------+------------------------------------------+
| Observation        | Record                                   |
+--------------------+------------------------------------------+
| Host rock          | What type of rock is it in/on?           |
|                    | (granite, basite, sandstone, schist...)   |
+--------------------+------------------------------------------+
| Geological setting | Vein, disseminated, massive, placer,     |
|                    | weathering surface, cave deposit          |
+--------------------+------------------------------------------+
| Associated         | What other minerals are nearby?           |
| minerals           | (quartz veins often host gold; iron       |
|                    | staining suggests oxidation zone)        |
+--------------------+------------------------------------------+
| Crystal form       | Visible crystals? Habit? Size?           |
| (if visible)       | (cubic, prismatic, tabular, massive)     |
+--------------------+------------------------------------------+

Got: Field context recorded before handling the specimen.

If fail: If geological context is unclear (loose specimen, urban find), proceed with physical properties only — context narrows candidates but is not required.

Step 2: Test Physical Properties

Apply the diagnostic tests systematically.

Diagnostic Property Tests:

LUSTER (how it reflects light):
- Metallic: reflects like metal (pyrite, galena, gold)
- Vitreous: glassy (quartz, feldspar)
- Pearly: like a pearl (muscovite, talc surfaces)
- Silky: like silk fibers (asbestos, satin spar gypsum)
- Earthy/dull: no reflection (kaolin, limonite)
- Adamantine: brilliant, diamond-like (diamond, zircon)

HARDNESS (Mohs scale — scratch test):
+------+-----------+----------------------------------+
| Mohs | Reference | Can Be Scratched By              |
+------+-----------+----------------------------------+
| 1    | Talc      | Fingernail                       |
| 2    | Gypsum    | Fingernail (barely)              |
| 3    | Calcite   | Copper coin                      |
| 4    | Fluorite  | Steel nail (easily)              |
| 5    | Apatite   | Steel nail (just)                |
| 6    | Feldspar  | Steel nail cannot scratch        |
| 7    | Quartz    | Scratches glass                  |
| 8    | Topaz     | Scratches quartz                 |
| 9    | Corundum  | Scratches topaz                  |
| 10   | Diamond   | Scratches everything             |
+------+-----------+----------------------------------+

Test: scratch the specimen with each reference tool, soft to hard.
Hardness sits between the tool that fails and the tool that succeeds.

STREAK (powder colour on porcelain):
- Drag the specimen firmly across an unglazed porcelain tile
- Record the colour of the powder line
- Streak colour is often different from specimen colour
- Critical: hematite is grey-black but streaks RED
- Critical: pyrite is gold but streaks BLACK
- Minerals harder than the streak plate (~7) leave no streak

CLEAVAGE AND FRACTURE:
- Cleavage: breaks along flat planes (mica: 1 direction, feldspar: 2)
- Fracture: breaks irregularly (conchoidal = curved like glass, uneven, fibrous)
- Note number of cleavage directions and angles between them

SPECIFIC GRAVITY (heft test):
- Hold the specimen and assess: heavier or lighter than expected for its size?
- Heavy: possible metallic ore (galena, gold, magnetite)
- Light: possible pumice, sulfur, or organic material

Got: A profile of the specimen: luster, hardness range, streak colour, cleavage/fracture type, and relative density.

If fail: If a property is ambiguous (e.g., luster between metallic and vitreous — "sub-metallic"), record both options. Ambiguity lowers confidence but does not block identification.

Step 3: Apply Special Tests

Additional tests for specific mineral groups.

Special Field Tests:

MAGNETISM:
- Hold a magnet near the specimen
- Strong attraction: magnetite (or possibly pyrrhotite)
- Weak attraction: some iron-bearing minerals

ACID TEST (10% HCl):
- Drop acid on the specimen surface
- Vigorous fizzing: calcite (CaCO3)
- Fizzing on powder only: dolomite (scratch surface first, then apply acid)
- No fizzing: not a carbonate

TASTE (only for suspected halite):
- Salty taste: halite (NaCl)
- Do NOT taste unknown minerals — some are toxic

SMELL:
- Sulfur: rotten egg smell (sulfides when scratched)
- Clay: earthy "petrichor" smell when breathed on (clay minerals)

TENACITY:
- Brittle: shatters when struck (most silicates)
- Malleable: deforms without breaking (gold, copper, silver)
- Flexible: bends and stays (chlorite, some micas)
- Elastic: bends and springs back (muscovite mica)

Got: Additional diagnostic data narrows identification further.

If fail: If special tests are unavailable (no magnet, no acid), proceed with basic properties — sufficient for most common minerals.

Step 4: Identify by Elimination

Cross-reference the property profile against known minerals.

Common Mineral Identification Key (simplified):

METALLIC LUSTER:
- Black streak + hard (6+) + cubic crystals = PYRITE
- Black streak + soft (2.5) + heavy + cubic = GALENA
- Red-brown streak + hard (5-6) + heavy = HEMATITE
- Yellow streak + soft (1.5-2.5) + yellow = GOLD (if malleable)
  or CHALCOPYRITE (if brittle, harder, green-black streak)
- Black streak + magnetic = MAGNETITE

NON-METALLIC, LIGHT-COLORED:
- Vitreous + hard (7) + conchoidal fracture = QUARTZ
- Vitreous + hard (6) + 2 cleavage planes = FELDSPAR
- Vitreous + soft (3) + fizzes in acid = CALCITE
- Pearly + very soft (1) + greasy feel = TALC
- Vitreous + soft (2) + 1 perfect cleavage = GYPSUM

NON-METALLIC, DARK-COLORED:
- Vitreous + hard (5-6) + 2 cleavage at ~90 degrees = PYROXENE
- Vitreous + hard (5-6) + 2 cleavage at ~60/120 degrees = AMPHIBOLE
- Vitreous + soft (2.5-3) + 1 perfect cleavage + flexible = BIOTITE (mica)

Got: A mineral identification or a shortlist of 2-3 candidates with the distinguishing test to differentiate them.

If fail: If the specimen matches no common mineral, it may be a rock (aggregate of minerals) rather than a single mineral, or it may require laboratory analysis (thin section, XRD).

Validation

• Field context was recorded before handling
• Luster was assessed under natural light
• Hardness was tested against at least two reference materials
• Streak colour was recorded (if specimen is softer than streak plate)
• Cleavage or fracture pattern was noted
• Identification was reached by systematic elimination, not guessing
• Look-alike minerals were explicitly considered and differentiated

Pitfalls

• Confusing pyrite with gold: "Fool's gold" (pyrite) is harder (6 vs 2.5), brittle (gold is malleable), and streaks black (gold streaks gold). The tests are definitive — use them
• Ignoring streak: Specimen colour is unreliable (hematite can be grey, red, or black). Streak colour is consistent and diagnostic
• Scratching with contaminated tools: A rusty steel nail produces a false streak. Clean test tools before use
• Assuming crystal habit: Many minerals rarely show well-formed crystals in the field. Massive or granular forms are more common — do not require visible crystals for identification
• Confusing weathered surface with true colour: Break the specimen to expose a fresh surface before testing. Weathering rinds can disguise the mineral beneath

Related Skills

• gold-washing — alluvial gold recovery uses mineral identification to read stream deposits and assess gold-bearing gravels