StoneyeMineral
The questions Stoneye asks, and the answer this mineral gives. A streak plate, a coin, a glass jar and a magnet cover most of them.
What colour is its streak?
red
Drag an edge of the stone hard across the unglazed back of a bathroom tile or a porcelain plate. The powder line it leaves is the streak, and it is often nothing like the colour of the stone itself. A stone harder than the tile leaves no line at all, and that is an answer too.
Does the stone scratch your fingernail?
Either
Its hardness range crosses this reference, so either answer keeps it in the running.
Drag a sharp edge of the stone once across your thumbnail, pressing firmly, then wipe the nail. A groove you can feel with another nail means yes. A soft white mark that wipes off is powder from the stone, not a scratch.
Does the stone scratch a copper coin?
No
Lay a copper coin flat on the table and drag a sharp edge of the stone across it once. Wipe the coin afterwards: a line that survives the wipe is a scratch, a smear that comes off is powder. Use a plain copper coin, because plated coins are harder than the copper they look like.
Does the stone scratch glass?
No
Lay a thick piece of glass, a jar or a bottle bottom, flat on the table and never hold it in your hand. Drag a sharp edge of the stone across it once, then wipe. A line you can feel with a fingernail is a scratch; a white smear that wipes away is powder from the stone.
Does the stone scratch a steel file?
No
The easy way round is to run the file across a corner of the stone instead. If the file bites and leaves a groove, the stone is the softer one, so answer no. If the file skates over it and leaves only a grey metal smear that wipes off, the stone is the harder one, so answer yes.
Does the stone scratch quartz?
No
Take a clear quartz crystal, or a piece you already know to be quartz, and lay it flat. Drag a sharp edge of the stone across one of its faces once, then wipe. Only a line that survives the wipe counts. If you have no quartz at hand, say you are not sure rather than guessing.
Does a magnet pull it?
not magnetic
Hang a fridge magnet from a thread and bring it slowly towards the stone. Strong means the stone jumps to the magnet; slight means the hanging magnet only leans towards it. Wipe the stone first, because iron dust from a hammer or a file makes any stone look magnetic.
How does the surface shine?
diamond-like, dull, earthy, or pearly
Turn the stone under a lamp or daylight and watch the reflection on a fresh, clean face. Metallic shines like polished steel and lets no light through its edge; glassy looks like the broken edge of a bottle. A dusty, weathered crust lies about the shine, so judge a broken face.
In how many directions does it break flat?
one direction
Hold a broken corner in raking light and count the directions in which flat, mirror-like faces repeat. Faces parallel to each other count as one direction. A curved, shell-like break is fracture, not cleavage: if that is all you see, this stone has no cleavage.
How heavy is it for its size?
normal for its size
Take an ordinary pebble of about the same size in your other hand and lift both. Heavy means clearly heavier than the plain stone; very heavy means it surprises you, the way a piece of lead does. Judge it against size, not against how big it looks.
| Erythrite | Cobaltite | |
|---|---|---|
| Streak | red | black or gray |
| Does the stone scratch a copper coin? | No | Yes |
| Luster | diamond-like, dull, earthy, or pearly | metallic |
| Cleavage | one direction | three directions, cubic |
| Heft | normal for its size | heavy for its size or very heavy for its size |
weathering crusts and hydrothermal veins
Photograph it with Stoneye for a shortlist, then narrow it down with the same tests. The app tells you when it is not sure instead of guessing.
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