Calcite

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Classic French specimen, a cluster of sharp rhombohedral calcite crystals impregnated with sand. In good condition.The Fontainebleau region, located in the Seine-et-Marne department of France, is characterized by its unique Oligocene-age sandstone and sand formations, which were deposited approximately 30 million years ago in a marine environment. These deposits are globally recognized for the occurrence of calcite, specifically in the form of "Fontainebleau sandstone," where large, poikilitic rhombohedral calcite crystals grew within the porous quartz sand matrix. Historically, the extraction of this material began centuries ago, with the stone being utilized for local building construction and industrial glassmaking. The scientific study of these specimens became prominent in the eighteenth and nineteenth centuries, as researchers documented how the calcite crystals enclosed the surrounding sand grains without disrupting their structure, a classic geological example of crystal growth within sedimentary host rock that continues to be a subject of interest for mineralogists today.