Rock Identifier alternatives — including one that is not an app

Determinative mineralogy runs on properties you test rather than properties you look at. All four are trivial to do at a kitchen table and none of them survives a photograph.

Streak. Rub the specimen on the unglazed back of a bathroom tile and look at the powder. This is the mineral's true colour with the optical effects stripped out, and it is nearly constant within a species. Hematite is the demonstration: silver, red or black specimens all leave the same rusty red-brown streak. It is also how you separate gold from pyrite in one second — gold streaks gold, pyrite streaks greenish-black.

Hardness. A fingernail is about 2.5 on the Mohs scale, a copper coin 3.5, a steel knife or window glass 5.5, a quartz pebble 7. Scratch a fresh face and rub the mark with a thumb before judging it — a steel blade drawn across quartz leaves a grey metal smear that looks exactly like a scratch and wipes off, meaning the mineral is harder than the steel.

Cleavage. How it breaks reflects how its atoms are bonded. Perfect cubes mean galena or halite; rhombs mean calcite; thin elastic sheets mean mica; curved shell-like fracture with no flat faces means quartz.

Heft. Density varies enormously and the hand is surprisingly good at it. Barite is the classic case — a colourless non-metallic mineral that is obviously too heavy, which is essentially its identification.

Add one drop of white vinegar, which separates the entire carbonate group in five seconds, and you have a kit that fits in a pocket and outperforms any camera. Our free mineral key is built around exactly these filters, and the Mohs scale tool explains what your scratch result means.

People reach for Seek or iNaturalist for a stone constantly, and it never works. The reason is structural rather than a gap somebody could fill: those apps are built on taxonomies of living things, contributed by naturalists and organised by biology. A rock has no place in a taxonomy of life.

The consequence is that the free, institution-backed, no-subscription option that exists for plants, birds and insects does not exist for minerals. There is no Cornell Lab of geology shipping a free scanner. That absence is why the paid rock apps have the space they do.

What does exist for free is better than an app anyway: Mindat is the largest mineral database in the world, free to search, with locality data down to individual mines, and it is what mineralogists actually use. It will not identify from a photograph — but combined with a streak plate and a hardness test it will get you further than any subscription.

Several apps in this category attach an estimated value to the identification, and that number deserves scepticism on its own terms.

Gemstone value is set by weight, colour grade, clarity grade, cut quality, treatment history and origin. A photograph gives you approximate colour and nothing else. Treatment in particular is the whole ballgame: essentially all blue topaz is irradiated, nearly all tanzanite is heated, and most emerald is oil-filled, and none of that is visible in an image.

Then there are the simulants. Cubic zirconia and moissanite are photographically indistinguishable from diamond, and moissanite is even harder than most gems — the classic "it scratches glass so it must be a diamond" test proves nothing, because quartz scratches glass too. What separates them is thermal conductivity and double refraction, one of which needs an instrument and the other a loupe.

The practical rule: treat any app valuation as entertainment. If a stone might genuinely be worth something, a gemmological laboratory report from GIA, AGS or an equivalent is the only number that means anything, and it costs less than being wrong. Our free gemstone key lists the simulants next to each real stone for that reason.

Everything the free keys on this site ask for costs less than one year of any app on this page.

• A white unglazed tile — the back of a bathroom tile, or the unglazed foot ring on the bottom of a mug. Free.
• A copper coin and a steel knife or nail — the two hardness reference points that matter most.
• A small bottle of white vinegar in a dropper. Separates the carbonates instantly.
• A 10× hand lens. The single most useful purchase in the whole of geology, and it costs a few pounds.
• A small magnet on a thread — magnetite is strongly magnetic, and a hanging magnet shows weak attraction that a held one hides.

Then break the specimen. Every description in every key refers to a fresh face, because weathering softens and discolours the outside of nearly everything, and a photograph of a weathered surface is a photograph of the weather.

Prices, in-app purchase tiers, ratings, versions and update dates are read from each app's US App Store listing on 2026-09-03 through Apple's Lookup API and product pages. Nothing here is typed from memory and the build fails if a price appears in the prose.

This page recommends a free browser tool over an app, including over our own. That is the honest conclusion for a subject where the decisive evidence is tactile: a streak plate reads a property a sensor cannot.