How do I find out what mineral I have?

Start with where the specimen came from, because the list of minerals known from that site narrows the answer faster than any test. Then work from the cheapest, least damaging observations to the more invasive ones: crystal shape (habit), luster, color, streak, hardness, cleavage and specific gravity. Stop when the candidates agree on every test, and send the piece to a lab when they do not. Expect to be wrong sometimes. The Mineralogical Society of America's identification key tells collectors that "if you find yourself correctly identifying 60% of the minerals you find, you will be doing well" [1]. Below are the order, what each step rules out, and three worked specimens.

The order that saves time and specimens

1. Locality first

A specimen labeled with a mine, quarry or collecting area comes with a built-in short list. Look the locality up on Mindat, where each locality page lists the species reported from it, and compare. A brassy cube from a site that lists pyrite and no gold is very probably pyrite. If your specimen has no locality, every later step has to work harder, and you should say so on the label. How to read a Mindat locality page, and how far to trust it, is on using Mindat and RRUFF.

The U.S. Geological Survey's old collector's leaflet makes the same point from the other direction: geologic maps are "unsurpassed as collecting guides" because they show where particular rock types occur, and most carry brief descriptions of them [3]. Knowing the rock tells you which minerals are possible.

2. Habit, under a lens

Habit means the shape a mineral's crystals usually take: cubes, six-sided prisms, needles, plates, rhombs, botryoidal (grape-like) crusts. The USGS leaflet recommends a hand lens of six to ten power for seeing mineral grains [3]. A clean six-sided prism ending in a point, glassy and colorless, points strongly to quartz before you have done any test at all.

3. Luster before anything else

Luster is the way the surface reflects light. The MSA key calls deciding it "the first critical step," and its first split is metallic, submetallic or nonmetallic, with nonmetallic subdivided into adamantine, resinous, glassy (vitreous), pearly, silky and earthy [2]. Mesa Community College's mineral lab gives the same instruction: "First determine the mineral's luster (metallic or non-metallic)" [4]. Luster terms, with examples, are explained on streak, luster and color.

4 and 5. Color, then streak

Color is the first thing you notice and the least reliable, because traces of impurity color many minerals. Streak, the color of the mineral's powder on an unglazed porcelain tile, is steadier. Hematite can be steel gray or black and still leaves a rust-red streak [5].

6. Hardness on a hidden spot

The Mesa lab sequence moves from luster to hardness, tested with a fingernail, a copper coin or a steel nail, and then to streak [4]. Scratch a hidden spot, wipe it, and record the result as a bracket ("harder than glass, softer than quartz"). The method and reference values are on testing hardness with the Mohs scale.

7. Cleavage and fracture

Cleavage is the tendency to split along flat planes set by the crystal structure. Galena breaks into cubes, with cleavage in three directions at 90 degrees, and calcite into rhombs with cleavage in three directions not at 90 degrees [6]. Quartz has no cleavage and breaks with a curved, shell-like (conchoidal) fracture [6]. Look at existing broken edges before you consider breaking anything.

8. Specific gravity

When two candidates survive the earlier tests and differ in weight, measure specific gravity. Barite at about 4.5 and calcite at 2.71 feel different in the hand and measure very differently [7]. The method, with a worked example, is on measuring specific gravity at home.

Tests to leave out

Some old field books and websites suggest tasting a mineral. Do not. Halite is salty, but so are other minerals, and the National Park Service's guidance on geological specimens names arsenic, lead, mercury, thallium and other toxic elements that occur in collection minerals [8]. That guidance advises neoprene gloves for minerals with potentially toxic elements, washing your hands afterward, and a respirator when cutting or trimming, because dust can be a greater risk than handling [8]. If a candidate on your list is a mercury, arsenic or lead mineral, skip the streak and hardness tests and read which minerals are dangerous first.

When to stop testing and send it to a lab

Stop when one of these is true:

• Two or three candidates fit every test you can run without damaging the piece.
• The answer matters for money: you plan to sell it, or it may be a rare species.
• The candidates include something you should not handle or powder.
• The tests disagree with each other or with the locality.

The MSA key warns that collectors should be "careful about depending too much on any one or two properties or tests," and that "even chemical and crystallographic tests have been known to fail" [1]. For unidentified specimens it suggests they may need to be "sent in to a professional lab in order to obtain a positive identification" [1]. What XRD and Raman can tell you, and what named labs charge, is on getting a specimen tested.

Three specimens, start to finish

A brassy cube from a coal-country road cut

• Locality: a road cut whose locality page lists pyrite and marcasite but no gold.
• Habit: sharp cubes with fine parallel lines (striations) on the faces. The SUNY Potsdam mineral tables describe pyrite as "cubic crystals, sometimes striated" [6].
• Luster: bright metallic.
• Streak: greenish black on the porcelain tile. Pyrite's streak is greenish or brownish black [6]; gold's is golden yellow [9].
• Hardness: scratches glass. Mesa's lab gives pyrite a hardness of 6 to 6.5 [4]; gold is 2½ to 3 and would be dented, not scratched, by steel [9].
• Answer: pyrite. No further test needed. Store it dry: the National Park Service notes that pyrite in humid air can release sulfur dioxide [8], and the conditions that cause decay are on pyrite decay.

A colorless crystal group from a limestone quarry

• Locality: a limestone quarry whose species list includes calcite, dolomite and quartz.
• Habit: pointed crystals, some broken pieces showing flat, slanted faces.
• Luster: glassy.
• Hardness: a steel nail scratches it; it does not scratch glass. Quartz, at 7, would scratch glass [10][11].
• Cleavage: broken edges show three sets of flat planes not at right angles, breaking into rhombs [6].
• Answer: calcite. Its hardness of 3, rhombic cleavage and glassy luster all agree [6][7]. (The page on common lookalikes explains why acid is not the test to reach for.)

A heavy gray cube from an old mine dump

• Locality: a dump in a lead-zinc district whose species list is led by galena and sphalerite.
• Habit and cleavage: silver-gray cubes; a loose fragment shows perfect cleavage in three directions at 90 degrees.
• Luster: bright metallic.
• Specific gravity: the piece feels far too heavy for its size. The MSA key gives galena an SG of 7.6 [9].
• Answer: galena, a lead mineral. Because it is a lead mineral, you can stop here: there is no need to powder it for a streak. Handle it with gloves, wash your hands, and label it as a lead mineral [8].

Writing down what you found

Whatever the result, record the tests and the outcome with the specimen's catalog number, and label an uncertain result as uncertain ("probably calcite"). If a later test shows you were wrong, correct the label without discarding the old one; how to do that is on when the label is wrong.

Narrowing the candidates with the identification key

Once you have luster, streak, hardness and a weight impression, the identification key takes those results and lists the species that match, with the next test to run. If you are still deciding between two familiar pairs, start with hardness, the test that settles more of them than any other.

References

1. Mineralogical Society of America, The Mineral Identification Key, "Conclusion & Organization" (undated, read October 2026). https://msaweb.org/msa/Collectors_Corner/id/mineral_id_keyi13.htm
2. Mineralogical Society of America, The Mineral Identification Key, "Mineral Properties & Luster" (undated, read October 2026). https://msaweb.org/msa/Collectors_Corner/id/mineral_id_keyi3.htm
3. U.S. Geological Survey, Collecting Rocks, INF-64-4 (1976 printing). https://www.michigan.gov/documents/deq/GIMDL-USGSCR_302981_7.pdf
4. Mesa Community College, Robert S. Leighty, GLG 101IN Lab 4: Minerals, Part D: Economic Minerals (undated, read October 2026). https://physci.mesacc.edu/Geology/Luther/GLG101IN/GLG101IN_Lab04_Minerals/GLG101IN_Lab04_Minerals5.html
5. Mineralogical Society of America, The Mineral Identification Key, Table IA: Minerals with metallic or submetallic luster and hardness of less than 2½ (undated, read October 2026). https://msaweb.org/msa/Collectors_Corner/id/mineral_id_keytia.htm
6. Michael Rygel and Page Quinton, Sedimentary Geology: Rocks, Environments and Stratigraphy (SUNY Potsdam), "14.1: Mineral Identification Tables," Geosciences LibreTexts, January 8, 2026, CC BY-SA 4.0. https://geo.libretexts.org/Courses/SUNY_Potsdam/Sedimentary_Geology%3A_Rocks_Environments_and_Stratigraphy/14%3A_Appendices/14.01%3A_Mineral_Identification_Tables
7. Mineralogical Society of America, The Mineral Identification Key, Table IIC-1: Streak not colored, cleavage prominent, hardness 2½ to 3 (undated, read October 2026). https://msaweb.org/msa/Collectors_Corner/id/mineral_id_keytiic1.htm
8. National Park Service, Greg McDonald, "Health and Safety Issues with Geological Specimens," Conserve O Gram 11/11, September 2006. https://www.nps.gov/subjects/museums/upload/11-11_508.pdf
9. Mineralogical Society of America, The Mineral Identification Key, Table IB: Minerals with metallic or submetallic luster and hardness greater than 2½ but less than 5½ (undated, read October 2026). https://msaweb.org/msa/Collectors_Corner/id/mineral_id_keytib.htm
10. Encyclopaedia Britannica, "Mohs hardness," revised and updated by Erik Gregersen, published 10 May 2025. https://britannica.com/print/article/387714
11. University of Notre Dame, Planet Earth laboratory, Mohs hardness scale handout (undated, read October 2026). https://www3.nd.edu/~cneal/planetearth/Lab-Mineral-ID/MOH.pdf