New Almaden hydrothermal deposition of cinnabar from deep within the earth is found in a gangue of silica-carbonate rock formed locally by hydrothermal alteration of serpentine. The Guadalupe mine produced about 10% as much mercury as the New Almaden. There are several smaller mines in the mining district, but their ore production was not significant. The only significant quicksilver ore is cinnabar; other sulfides are present in small quantities. Mining, other than a single placer deposit of cinnabar, was underground. There is a high probability of undiscovered high-grade ore which could be found and exploited using modern techniques. Mining operations resulted in
Cinnabar ("kinnabari"), a Greek word most likely applied by Theophrastus to several distinct substances. Other sources say the word comes from the "shangarf" (Arabicized as "zinjifra"), a word of uncertain origin. In Latin, it was sometimes known as "minium", meaning also "red cinnamon", though both of these terms now refer specifically to lead tetroxide. Cinnabar is generally found in a massive, granular or earthy form and is bright scarlet to brick-red in color, though it occasionally occurs in crystals with a nonmetallic adamantine luster. It resembles quartz in its symmetry. It exhibits birefringence, and it has the highest refractive index of