LithoMap

Evidence before labels

Rock and mineral field tests

Learn what each test measures, how to perform it carefully, how to interpret ambiguous results, and when to stop. Use the methods together: a single scratch, streak, fizz, or magnetic response is never a complete identification.

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Six practical methods

Choose the next useful observation

Start with nondestructive observation. Add the least destructive test that can separate your leading possibilities, then record the exact result rather than jumping directly to a name.

01

Hardness

A careful scratch comparison can place a mineral within a useful hardness range, but weathering, grain size, coatings, and confusion between a scratch and a powder mark can produce false results.

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02

Streak

Streak records the color of a mineral’s powder and can be more consistent than surface color, especially for metallic and iron-bearing minerals.

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03

Breakage

Breakage pattern is often more reliable than color, but one shiny flat surface is not enough: cleavage must repeat with consistent orientation across the same mineral.

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04

Acid reaction

Acid effervescence is a useful carbonate clue, but chemical handling, coatings, powdered tests, and mixed rocks make it a controlled last-step test rather than a casual first check.

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05

Magnetism

Magnetic response can quickly separate some iron-bearing minerals, but grain size, intergrowths, weathering, and magnet strength make it a supporting property rather than a complete identification.

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06

Density

Heft is a useful first impression, but a simple hydrostatic measurement provides stronger evidence for unusually dense minerals when porosity, trapped bubbles, and water-sensitive material are controlled.

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A defensible sequence

Observe first. Test second. Conclude last.

Apply the results in the rock identification guides or mineral identification guides. If you do not yet have a likely match, start with the interactive identification tool.

  1. Describe the specimen. Record texture, grain size, luster, color, form, and breakage before changing it.
  2. Choose a discriminating test. Ask which observation would separate the few possibilities you already have.
  3. Use a clean representative spot. Avoid coatings, weathered rind, attached matrix, polished faces, and mixed grains.
  4. Record uncertainty. A bracket, weak response, or unavailable test is more useful than a confident guess.
  5. Seek confirmation when stakes matter. Valuable, hazardous, regulated, or scientifically important material deserves expert or laboratory review.

Protect the specimen, yourself, and the place

Do not taste minerals. Avoid unnecessary dust, destructive testing, unknown mine waste, unstable excavations, and unauthorized collection. National parks generally prohibit recreational rock and mineral collecting; other public and private lands have their own restrictions. Confirm the current rule with the responsible land manager.

National Park Service collecting guidance · Bureau of Land Management rockhounding guidance