Much of the mineral wealth found in San Diego County comes from pegmatite deposits. Pegmatite is a coarse-grained igneous rock that forms late in the emplacement of a usually granitic magma. Some magmas contain rare elements such as beryllium, lithium, boron, fluorine and phosphorus, which tend not to form minerals easily. As the magma cools and crystallizes out "normal" rock-forming minerals such as quartz and feldspar, these rare elements get more and more concentrated---to the point that "something just has to happen"---and minerals such as beryl, tourmaline, topaz and spodumene form. Fortunately in many cases in San Diego County, these late-stage minerals also formed as well-developed crystals in a fluid environment that allowed them to do so.
The most prolific locality in the area is probably the Himalaya mine with its intermittent but relatively profuse production of mostly pink elbaite over the last century.
Without question the finest specimens of elbaite tourmaline ever recovered in North America were found at the Tourmaline Queen Mine in 1972. Prior to that discovery, the Tourmaline Queen Mine had certainly been a known producer of elbaite since it was first worked early in the twentieth century, but the discovery of the "blue cap" pocket launched it into legendary status. The name "blue cap" is in reference to the thin ink-blue zone that caps the tops of all of the crystals found in the pocket.
More recently, a significant find of elbaite was made at the Cryo-Genie mine. Specimens consist of floater and matrix specimens of tapered, commonly doubly terminated crystals with pastel green to pink zoning.
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Tourmaline / (Doubly-terminated “Floater”)
Himalaya Mine, Mesa Grande, San Diego County, California
