Farm Hill No. 2 Mine (Emerald Lake; Challenge Mine), San Mateo Co., California, USA
REF:Deposit:: CDMG. JOUR. MINES & GEO. V. 51, NO.4, OCT, 1955, P.415, PL.
Deposit:: INF. SERVICE. V. 10, NO.2, 457, P.10.
Commodities (Major) - Mercury
Development Status: Past Producer
The existence of mercury mineralization at the site has been known since 1863, but only after being rediscovered in 1953 was it mined. The area is in the central part of an irregular mass of serpentine, which at the surface has weathered to an ocherous clay. Below this clay, cinnabar coats fracture surfaces in silica-carbonate rock and the surrounding tuff and shale of the Franciscan formation. Cinnabar, metacinnabar, and native mercury occur in vugs and along fracture surfaces in the rock. Eglestonite,terlinguaite,calomel and native mercury are also present in the ore. Very rare wattersite has been identified in some samples (R. Erd, 1990). Montroydite rarely occurs with the native mercury. The area is now largely covered by streets and houses, but some cinnabar-bearing exposures are in an adjoining city park.
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Map Reference: 37°27'13"N , 122°15'1"W
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Mineral List:10 entries listed. 10 valid minerals.
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