Watch a video of this specimen by following the Vimeo link below: https://vimeo.com/940670613 Sand-calcite is an uncommon variety of calcite resulting from the growth of a calcite crystal in a sandy sediment. The sand grains are incorporated into the crystals, hence forming euhedral calcite crystals totally filled with sand! The Fontainebleau sandstones, lying underneath the eponymous forest south of Paris, are the historical deposit for some of the sharpest and purest sand-calcite crystals known in the world. In particular, the 'Bellecroix' sand-calcites have been amazing naturalist scientists since their discovery in the late XVIIIth century: they were first described in 1777 by de Lassone (1717-1788), royal doctor of Queen Marie-Antoinette and King Louis XVI (just before the Revolution), shortly after the mining of the sandstone layers for construction rock purposes hit a cave full of sand-calcite crystals in 1774! You have here a nice and old specimen from one of the few 'pocket caves' found over the centuries near Bellecroix. It consists in a floater cluster of twinned scalenohedral sand-calcite crystals, showing this totally distinctive very clear white-gray sand colour featuring very thin and homogeneous grain size, allowing for a sharp crystal growth. A beautiful historical French classic.