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Hilton deposit, Borrego Springs, San Diego County, California, USAi
Regional Level Types
Hilton depositDeposit
Borrego SpringsGroup of Springs
San Diego CountyCounty
CaliforniaState
USACountry

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Key
Latitude & Longitude (WGS84):
33° 17' 54'' North , 116° 6' 34'' West
Latitude & Longitude (decimal):
Locality type:
Nearest Settlements:
PlacePopulationDistance
Salton Sea Beach422 (2011)12.4km
Desert Shores1,104 (2011)13.4km
Salton City3,763 (2011)14.3km
Oasis6,890 (2011)18.6km
Borrego Springs3,429 (2014)25.1km


A former Ca mine located about 16 miles ENE of Borrego Springs near the Imperial County line.
A calcite (Iceland spar) mine located in the S½ sec. 14, and in the S½ sec. 15, T10S, R8E, SBM, 14.9 km (9.2 miles) W of Salton City (Imperial County) on the S slope of the Santa Rosa Mountains in the Anza Borrego Desert State Park. The Navy called this location Hilton Calcite Mine, today it is commonly called Calcite Mine. This was the only location in the U.S. where optical Calcite (Iceland Spar) was mined during W.W.II for strategic purposes. The mining process was similar to gem extraction.

NOTE: Coordinates provided are approximate at the center of the 3 areas worked in the 1940’s.

The workings comprised about 75 trenches in 3 areas: Central (center at approx. N33.29761 W 116.10894), Heather (center at approx N 33.30137 W 116.10941) and Defiance (center at approx N 33.29844 W 116.11144) on approx. 30 acres. Some trenches are still visible.

The main working area is at N33.29895 W116.10995, elevation 1140 ft, where the calcite was prepared for the transport in small trucks down the treacherous 2 Miles to the Truckhaven road. In 2005 the road was washed out and off-camber but navigable with a high clearance 4x4 and an experienced driver.

The land was originally owned by John W. Hilton (1904-1983), a gemologist, botanist, geologist, miner, zoologist, and adviser to Gen. George S. Patton, and a well-known landscape painter. Hilton, with Dr. Harry Berman, a mineralogist from Harvard, discovered the “optical” calcite (Iceland Spar), a special form of calcite in 1936. This high-grade calcite crystal improved the targeting accuracy of bomb sights (ring sights, see description in Desert Magazine Oct 1950) and anti-aircraft weaponry; it thereby raised the survival rate of allied bombing patrol missions. Hilton and his friend, Guy Hazen, first mined the calcite themselves, but in 1942 sold the mine to the Polaroid Corp. (under contract to the Navy), which employed up to 30 miners. The Navy constructed the Jeep Trail to the mine.

About 6,800 pounds of sub-optical grade calcite was shipped by Polaroid Corporation of Cambridge, Massachusetts, from material mined from the deposit during 1942-1944 and was used for the production of the “Polaroid Optical Ring Sight” invented by Edwin H. Land.

If John W. Hilton had been a better businessman, optical calcite could have made him rich, but he believed himself part of the greater war effort and refused to ask the Navy for more money.

In 1944 a synthetic substitute was invented and mining stopped around 1945.

Scientists believe that the Vikings have used Iceland Spar as a navigational aid. Owing to the crystal’s unusual property of creating a double refraction of sunlight, the sun’s position can be pinpointed with remarkable accuracy simply by rotating it against the human eye until the darkness of the two shadows become equal. Researchers say the principle holds true even when obscured by thick cloud or fog.

The process involves moving the stone across the visual field to reveal a yellow entoptic pattern on the fovea of the eye, probably Haidinger's brush. The recovery of an Iceland spar sunstone from the Elizabethan ship Alderney that sank in 1592 suggests that this navigational technology may have persisted after the invention of the magnetic compass.

The deposit also appears to have been called Calcite Operators Inc. Mine; Calcite Mine; Palm Wash Calcite Field.

Select Mineral List Type

Standard Detailed Strunz Dana Chemical Elements

Mineral List


1 valid mineral.

Detailed Mineral List:

Calcite
Formula: CaCO3
Description: Occurs as broad, flat plates to 1 foot (0.3 meters) diameter of optical-grade material.
Reference: Wright, L.A. (1957) Calcite (optical grade) California Division of Mines and Geology Bulletin 176: 99-100. Weber, F.H. Jr. (1963) Mines and mineral resources of San Diego County, California. California Division of Mines and Geology County Report 3, 309 pp.: 52-54. Murdoch, J., Webb, R.W. (1966),Minerals of California, Centennial Volume (1866-1966): California Division Mines & Geology Bulletin 189: 118. Pemberton, H.E. (1983) Minerals of California. Van Nostrand Reinholt Press: 211.
Calcite var: Iceland Spar
Formula: CaCO3
Description: Occurs as broad, flat plates to 1 foot (0.3 meters) diameter of optical-grade material.
Reference: Wright, L.A. (1957) Calcite (optical grade) California Division of Mines and Geology Bulletin 176: 99-100. Weber, F.H. Jr. (1963) Mines and mineral resources of San Diego County, California. California Division of Mines and Geology County Report 3, 309 pp.: 52-54. Murdoch, J., Webb, R.W. (1966) Minerals of California, Centennial Volume (1866-1966): California Division Mines & Geology Bulletin 189: 118. Pemberton, H. E. (1983) Minerals of California. Van Nostrand Reinholt Press: 211.

List of minerals arranged by Strunz 10th Edition classification

Group 5 - Nitrates and Carbonates
Calcite5.AB.05CaCO3
var: Iceland Spar5.AB.05CaCO3

List of minerals arranged by Dana 8th Edition classification

Group 14 - ANHYDROUS NORMAL CARBONATES
A(XO3)
Calcite14.1.1.1CaCO3
Unclassified Minerals, Mixtures, etc.
var: Iceland Spar-CaCO3

List of minerals for each chemical element

CCarbon
C Calcite (var: Iceland Spar)CaCO3
C CalciteCaCO3
OOxygen
O Calcite (var: Iceland Spar)CaCO3
O CalciteCaCO3
CaCalcium
Ca Calcite (var: Iceland Spar)CaCO3
Ca CalciteCaCO3

References

Sort by

Year (asc) Year (desc) Author (A-Z) Author (Z-A)
Weber, F.H., Jr. (1963) Mines and mineral resources of San Diego County, California; California Division of Mines and Geology, County Report 3, 309 pp.: 52-53, Pl. 1.
Durrell, Cordell (1944) Report on the Calcite Mines in Northeast San Diego County. In: USGS Open-File Report 77-685.
Hilton, J.W. (1950) Mining for Gunsights. Desert Magazine, p. 5, October 1950.
Wright, L.A. (1957) Calcite (optical grade). California Division of Mines and Geology Bulletin 176: 99-100.
Murdoch, J. and Webb, R.W. (1966) Minerals of California, Centennial Volume (1866-1966). California Division Mines & Geology Bulletin 189: 118.
Wood, E.A. (1977) Crystals and Light: An Introduction to Optical Crystallography.
Gilluly, J. (1977) Calcite deposits in Imperial and San Diego counties, California: Calcite deposits near Truckhaven, Imperial County, California. USGS Open-File Report:77-685-A.
Pemberton, H.E. (1983) Minerals of California. Van Nostrand Reinhold Press: 211.
Orrell, L. (1993) Mining California Crystals for the Optical Ring-Sight. California Geology, May/June 1993.
Coghlan, A. (2011) Vikings' crystal clear method of navigation. New Scientist, Issue 2798.
Ropars, G. Gorre, G., Le Floch, A., Enoch, J., and Lakshminarayanan, V. (2011) A depolarizer as a possible precise sunstone for Viking navigation by polarized skylight. Proceedings of the Royal Society, A, 468(2139), 671-684.

Other Regions, Features and Areas containg this locality

North America
Pacific PlateTectonic Plate

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