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Farm Hill No. 2 Mine (Emerald Lake Mine; Upper Emerald Lake deposit), Upper Emerald Lake, Emerald Lake Hills, San Mateo Co., California, USA

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A former Hg mine located in the W½ sec. 36, T5S, R4W, MDM, 2.0 km (6,500 feet) SE of Emerald Lake Hills, about 3/8 mile SE of Upper Emerald Lake, near Redwood City.

The existence of mercury mineralization at the site has been known since 1863, but only after being rediscovered in 1953 during site work for a housing development, was it mined.

Fragments of cinnabar and metacinnabar were found in top soil. 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.

Mineral List

8 entries listed. 8 valid minerals.

The above list contains all mineral locality references listed on This does not claim to be a complete list. If you know of more minerals from this site, please register so you can add to our database. This locality information is for reference purposes only. You should never attempt to visit any sites listed in without first ensuring that you have the permission of the land and/or mineral rights holders for access and that you are aware of all safety precautions necessary.


Davis, Fenelon Francis (1955), Mines and mineral resources of San Mateo County, California: California Journal of Mines and Geology: 51(4): 401-458, Pl. 5.

Mineral Information Service (1957) California Division of Mines: 10(2): 457: 10.

Holmes, Jr., G.W. (1965), Mercury in California: in: U.S. Bureau of Mines Information Circular 8252: 127.

Murdoch, Joseph & Robert W. Webb (1966), Minerals of California, Centennial Volume (1866-1966): California Division Mines & Geology Bulletin 189: 150, 260, 262, 362.

Pemberton, H. Earl (1983), Minerals of California; Van Nostrand Reinholt Press: 121-122.

Erd, R. (1990).

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