Identifying an unknown, in order

A sequence, cheapest and most informative first. Most specimens are named before the bottom.

Work down this

Each step narrows the field. Do them in order, because the early ones are free and the later ones are destructive or expensive.

Step one is not a test

1 · Locality. If you know where it came from, look up what occurs there. This eliminates more possibilities than every physical test combined, and it costs nothing.

2 · Habit and form. Cubic, prismatic, tabular, acicular, botryoidal, massive. For many species this alone is diagnostic.

3 · Associated species. Minerals occur in assemblages, and what it is sitting on narrows the answer.

4 · Color, lustre, transparency. Weak alone, useful in combination.

The physical tests

5 · Streak, on an unglazed tile. Fast, definitive for many opaque species, and it costs a fragment.

6 · Hardness, by scratch against known references. On an inconspicuous spot, never a crystal face, and scratch the unknown with the reference rather than the reverse.

7 · Cleavage and fracture, observed on an existing break rather than a fresh one.

8 · Specific gravity, which is quantitative, undervalued and needs only a scale and water.

9 · Magnetism, and fluorescence under both long and short wave.

10 · A dilute acid drop for carbonates, on a hidden spot, rinsed afterwards.

Stop and record

When you have a name, write it with how you got there: "habit, streak and hardness" or "locality and association".

When you do not, write "unknown" and the tests you ran. That is a complete and useful entry, and it is far better than a guess.

For anything you intend to sell as a rarity, instrumental analysis through a university department or a commercial lab is the answer, and its result goes on the label as the basis.

References