Detecting & Rocks Tools
Metal detecting, coin composition, melt value and rockhounding.
Work out the metal value of coins from weight, fineness and spot price — and the legal and practical limits on acting on it.
US Coin Composition TimelineWhen each coin's metal content changed, and why — the dates that decide whether a handful of change is worth sorting.
Rock and Mineral Identification KeyHardness alone identifies 2 of 39 minerals. Add specific gravity and it is 21. Colour identifies almost nothing.
Specific Gravity CalculatorWeigh it dry, then in water. The units cancel, so grams or ounces give the same answer — it is a ratio, not a weight.
Gem Carat Weight EstimatorA 1ct diamond cut shallow shows 17% more face-up area than the same weight cut deep. Carat is a weight, not a size.
Rock Tumbling Grit ScheduleEvery grit step in a working schedule is a 4x drop. The step into polish is 19x, which is where dull stones come from.
Gold Panning Yield CalculatorA visible flake of gold is worth about seven cents. Panning good ground by hand earns $4.58 an hour, and the arithmetic says why.
Metal Detector Settings GuideYou cannot discriminate out pull-tabs without losing gold rings — they read the same. Frequency and coil size are trades, not qualities.
Arrowhead & Fossil IdentificationMost arrowheads are not arrowheads. The bow reached North America only 1,500 years ago — neck width tells you what you actually have.
Find Log & Collection CatalogRecord finds with location, depth and context, then print display labels. Coordinates blur before they leave your browser.
About these detecting & rocks tools
The Mohs hardness scale is ordinal, not linear, and treating it as linear gives a badly wrong picture of the top end. Each step means only that the higher number scratches the lower one. On an absolute scale, talc at 1 is about 1, corundum at 9 is around 400, and diamond at 10 is roughly 1,500 — so the single step from 9 to 10 is a bigger jump than the whole distance from 1 to 9. The practical use of the scale is the field test rather than the number: a fingernail is about 2.5, a copper coin about 3.5, a steel knife blade about 5.5, and window glass about 5.5 too. Working out which of those a specimen will and will not scratch narrows the field faster than any amount of looking, and it costs nothing. The second thing worth knowing, on the detecting side, is that discrimination settings are a trade rather than a filter. Rejecting the signal range that iron occupies also rejects a good deal of non-ferrous metal that happens to read there, and iron close to a target can mask it entirely. Heavily discriminated searching over a productive site reliably leaves things behind, which is why the same field can be worked repeatedly by different people and keep producing. The third is that ground mineralisation moves everything. Soil rich in iron oxides shifts target readings and cuts depth, and a machine that has not been ground-balanced to the site is working with numbers that mean something different from what the manual says.