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California State Gem Mine (Dallas Gem Mine; Benitoite Mine; Benitoite Gem Mine; Gem Mine), Dallas Gem Mine area, San Benito River headwaters area, New Idria District, Diablo Range, San Benito Co., California, USA

This page kindly sponsored by Jim Bean
Latitude & Longitude (WGS84): 36° 20' 9'' North , 120° 36' 19'' West
Latitude & Longitude (decimal): 36.33611,-120.60528
Köppen climate type:Csb : Warm-summer Mediterranean climate

A former gemstone and specimen mine located in the NE¼ sec. 25, T18S, R12E, MDM, 1.2 km (4,000 feet) SSW of Santa Rita Peak at the headwaters of the San Benito River and New Idria, W side of the Diablo Range, about 25 miles N of Coalinga.

Mineralization is natrolite veins cutting a glaucophane schist inclusion in a serpentinite body.

Note: The majority of specimens from this locality have been prepared by dissolving away the enclosing natrolite with hydrochloric acid.

Mineral List

31 valid minerals. 6 (TL) - type locality of valid minerals.

Rock Types Recorded

Note: this is a very new system on and data is currently VERY limited. Please bear with us while we work towards adding this information!

Select Rock List Type

Alphabetical List Tree Diagram

Regional Geology

This geological map and associated information on rock units at or nearby to the coordinates given for this locality is based on relatively small scale geological maps provided by various national Geological Surveys. This does not necessarily represent the complete geology at this locality but it gives a background for the region in which it is found.

Click on geological units on the map for more information. Click here to view full-screen map on

Late Jurassic - Middle Jurassic
145 - 174.1 Ma

ID: 2881475
Ultramafic rocks, chiefly Mesozoic, unit 3 (Coast Ranges and Western Klamath Mountains)

Age: Jurassic (145 - 174.1 Ma)

Stratigraphic Name: Josephine Peridotite

Description: Ultramafic rocks, mostly serpentine. Minor peridotite, gabbro, and diabase. Chiefly Mesozoic unit 3

Comments: Coast Range ophiolite, Josephine ophiolite. Ultramafic rocks in Middle to Late Jurassic ophiolites of Coast Ranges and westernmost Klamath Mts.

Lithology: Major:{serpentinite}, Minor:{peridotite}

Reference: Horton, J.D., C.A. San Juan, and D.B. Stoeser. The State Geologic Map Compilation (SGMC) geodatabase of the conterminous United States. doi: 10.3133/ds1052. U.S. Geological Survey Data Series 1052. [133]

Data and map coding provided by, used under Creative Commons Attribution 4.0 License

This page 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.


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Louderback, G.D. and Blasdale, W.C. (1907) Benitoite, a new California gem mineral, with chemical analysis by Walter C. Blasdale. University of California, Department of Geological Sciences Bulletin: 5: 149-153.
Arnold, R. (1908) Notes on the occurrence of the recently described gem material, benitoite. Science, new series: 27: 312-314.
Ford, W.E. (1909) Neptunite crystals from San Benito, California. American Journal of Science, 4th. Series: 27: 235-240; […Zeitschr. Kristallographie, Band 46: 321-325 (1909)].
Louderback, G.D. and Blasdale, W.C. (1909) Benitoite, its mineralogy, paragenesis and mode of occurrence. University of California, Department of Geological Sciences Bulletin: 5: 331-380; 331, 354, 357, 359, 360, 361, 363, 376, 380.
Schaller, W.T. (1911) Notes on neptunite. USGS Bulletin 490: 55-57.
Palache, C. and Foshag, W.F. (1932) The chemical nature of joaquinite. American Mineralogist: 17: 308-312.
Buttgenbach, H. (1937-38) Sur un crystal de neptunite. Annales de la Société Geologique de Belgique: 61: 324-325.
Murdoch, J. and Webb, R.W. (1966) Minerals of California, Centennial Volume (1866-1966). California Division Mines & Geology Bulletin 189: 64, 70, 72, 82, 102, 130, 169, 182, 234, 277, 279, 298, 309.
Potter, R.W. and Evans, H.T. (1976) Definitive X-ray powder data for covellite, anilite, djurleite and chalcocite. USGS Jour. Res.: 4: 205-212.
American Mineralogist (1976) 51: 381-387.
Wise, W.S and Gill, R.H. (1977) Minerals of the Benitoite Gem mine. The Mineralogical Record 8, 442-452.
Wise, W.S. and Pabst, A. (1977) Jonesite, a new mineral from the Benitoite Gem mine, San Benito County, California. The Mineralogical Record 8, 453-456.
Wise, W.S. (1982) Strontiojoaquinite and bario-orthojoaquinite: two new members of the joaquinite group. American Mineralogist 67: 809-81.
Pemberton, H.E. (1983) Minerals of California. Van Nostrand Reinholt Press: 98, 100, 216, 362, 372, 392, 399, 403, 410, 466, 467, 470, 472.
Ma, C. and Rossman, G.R. (2008) Barioperovskite, a new mineral from the Benitoite Mine, California. American Mineralogist: 93: 154-157.

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