Datolite
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Datolite is a calcium boron hydroxide nesosilicate, CaBSiO4. It was first observed by Jens Esmark in 1806, and named by him from δατεῖσθαι, "to divide," and λίθος, "stone," in allusion to the granular
Datolite on sphalerite from San Luis Potosí, Mexico (size: 6.2 x 5.3 x 2.8 cm)
Polished datolite nodule from the Quincy Mine of Michigan’s Copper Country (size: 4.1 x 3.3 x 1.7 cm)
Mohs scale
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The Mohs scale of mineral hardness is a qualitative ordinal scale, from 1 to 10, characterizing scratch resistance of minerals through the ability of harder material to scratch softer material.
Mohs hardness kit, containing one specimen of each mineral on the ten-point hardness scale
Talc block
Gypse Arignac
Calcite sample 2