“"Called this quartz in Oviedo Diamante de las Caldas, because of its crystalline form, its hardness and abundant near those thermal waters. It appears with all the characters of the rock crystal, except its color that is brown and sometimes black, lustrous and vitreous, that color must come from a volatile or carbonaceous substance, because it disappears by the action of heat. It occurs in loose crystals, perfectly finished or well implanted in the limestone rock in which they lie, and that disintegrated by the action of Atmospheric agents releases the smoky quartz crystals, which, carried away by the waters, are taken to points more or less far from the area of ​​their deposit. The name of Jacintos de Compostela that some have assigned to them is not exact, as well as the fact that the name of these is improper, because they have not been in Santiago de Galicia, the color of the jacintos is not black, like that of our diamantes, if not red. " Mineralogía Asturiana. Máximo Fuertes Acevedo. 1880. ”