Elbaite from southern California, U.S.A.

--- pink tourmaline in aplite host

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Figures 1-2.
Left: bright pinkish-red elbaite prisms in a matrix that has aplitic (sugary, fine-grained) texture and is most probably pale lepidolite mica and granular albite (variety cleavelandite) feldspar plus quartz. The prisms have attractive colour but do not appear, to the naked eye, to be compositionally zoned, either across or along the prism length (c-axis) of the crystals.
Right: a close-up of the sample. The elbaite prisms average circa 1 cm in length, the matrix grain size is 1 mm and below. The aplite matrix is typically described as having a saccharoidal (sugary) texture. Note that my observations and photographs were made through the display cabinet glass, so are hardly ideal. This sample (ME-460) is in the excellent collection of the Miller Museum, Queen's University, Kingston, Ontario, an eclectic and delightful exhibit that will impress and instruct any dedicated rockhound.

This "Rock of the Month" is dedicated to Mark Badham, for 32 years the curator at the Miller Museum, who moves on in April 2018. The fine modern display cases, as well as the marvellous mixture of old and new exhibits, that I find fascinating, can be ascribed to Mark's tenure at Queen's. Thank You and Best Wishes, Mark!

"Rock of the Month #202, posted for April 2018" ---


is a frequently spectacular, colourful end-member of the borosilicate (cyclosilicate) tourmaline family (and tourmaline is by far the most common borosilicate mineral: currently with 1,904 records in the MINLIB bibliography, cf. 117 for axinite, 86 for dumortierite and 80 for datolite). The pink variety of elbaite seen here is called rubellite. Other varietal names are blue indicolite, green verdelite and clear achroite. Elbaite is often zoned from end to end, a reflection of the piezoelectric nature of tourmaline, and classic specimens exhibit "watermelon" hues (green to pink), rarely with deep blue terminations. As a tourmaline, elbaite is very hard (Mohs 7.5) and the prisms are typically striated. The mineral formula is Na(Li1.5Al1.5)Al6(Si6O18)(BO3)3(OH)4.Many of the finest specimens have been won from pegmatites in Afghanistan, Brazil, and southern California. The colour zoning, size and clarity of the striated prisms of tourmaline make this mineral, and especially elbaite, a darling of the mineral collecting world, especially in terms of the high-end specimens. In recent years, I'll guess that there have probably been more coffee-table books and collector-magazine articles on elbaite than on any other gemstone (see, e.g., Falster et al., 2002; Mauthner, 2015).


The labelling on the specimen, at the time of my last visit to the Miller Museum in 2017, does not state the locality. However, the combination of pinkish-red tourmaline and pale lilac mica-rich aplite host is very distinctive. I can think of just two likely possibilities, but since I have not visited either locality I cannot be personally sure of the provenance (I studied 1 or 2 thin sections from Meldon during my analyses of Cornish tourmalines, for my long-ago thesis, but do not recall seeing the hand specimen). The two ideas for locality are:

San Diego county, southern California, U.S.A.

The gem pegmatites of southern California include the Tourmaline Queen mine, on the east flank of Pala Mountain (aka Tourmaline Queen Mountain), in northern San Diego county (Swoboda, 2002; see also Barlow et al., 1996; Wilson, 2014), and the Himalaya mine (Mauthner, 2015). More fine elbaite has been won from the Stewart mine (Stewart Lithia mine, later re-opened as a gemstone mine, also on Tourmaline Queen Mountain) and the Tourmaline King mine, both in the Mesa Grande district (Wilson, 2007). The pegmatite dykes at the Stewart mine are of Cretaceous age. Mineralogically-banded "line rock" occurs in some evolved granitoids, such as the aplite portion of the George Ashley Block in the Pala pegmatite district. In this 8-m-thick composite pegmatite- aplite dyke, there is rhythmic layering, with garnet-rich bands alternating with albite- quartz- muscovite- rich bands. Cumulus (settling) textures are notably absent from the layered rock and the texture may form by an in-situ diffusion-controlled process of oscillatory nucleation and crystallization (Webber et al., 1997).

Meldon aplite quarries, near Okehampton, Devon, England

The two Meldon quarries have long been noted for their interesting associations of minerals. Although lithium-mica granites are common in Cornwall, other Li minerals found at Meldon, such as petalite and spodumene (McLintock, 1923; Drysdale, 1985), are not at all common. Meldon is known to host both rubellite and lepidolite (Dearman, 1962). An ion microprobe study of Li in tourmaline and quartz across Cornwall showed generally lower levels of the element, typically with 140 to 1700 ppm Li (up to 0.37 wt.% Li2O) in tourmaline and 26-210 ppm in quartz (Wilson, 1980). Note that these are the common schorl and dravite (Fe and Mg-rich) compositions of tourmaline, black to brown in colour, not elbaite with its essential Li in the formula. Micas contain far more Li than most tourmaline (Henderson et al., 1989), as of course do the discrete Li minerals observed at Meldon. Located on the northwestern edge of the Dartmoor massif, the quarries display the interaction of the Hercynian granite batholith of southwest England with predominantly sedimentary host rocks such as shale, quartzite and chert (Anon, 2007).


The evidence favours the Stewart Lithia mine, even though other pegmatites around the world contain both rubellite and lepidolite, e.g., Varutrask in Sweden (Quensel and Gabrielson, 1939) and Urubu in northern Minas Gerais, Brazil (Cassedanne and Cassedanne, 1981). With all due thanks to colleagues I have consulted, their experience is conclusive: the Stewart mine in the Pala district, San Diego county, California, is the source of this sample. Such material is widespread in collections: I noted a similar piece (sample 4814) at the Yifu Museum, China University of Geoscience-Beijing, in 2016. According to pegmatite expert Mark I. Jacobson, such specimens were extracted from outcrop at the mine in 1892, and sold into collections around the world. The specimens were an immediate commercial success (Fig. 3) and multiple adverts appeared to sell the goods. Tonnes of specimens were shipped out, hence their wide distribution to this day (Figs. 4-5). The interesting early days of the gemstone mining in southern California are recounted in some detail by Jacobson (2017).

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Figure 3.
Advertisement for the hot new thing, the remarkably pretty elbaite on lepidolite from the Stewart Lithia mine, published by the well-respected dealership of A.E. Foote in the American Journal of Science, series 3, volume 43, inside front page, in April 1892, as the production of the gemmy stones was rapidly ramped up. Advert republished in Jacobson (2017).

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Figures 4-5. Left: an historical specimen, displayed and illustrated in 1903. Figure supplied by Mark Jacobson.
Right: Another piece that has the aspect of the earliest (1880s) finds. Quite a large example, some 13x8inches (33x20 cm) in size, this was recovered by Mark Jacobson in 1986 from loose boulders (the early material was in outcrop, unlike more recent mined specimens, hence this boulder find has the look of the classic specimens). Published in Jacobson (2017).

The association of Aplite and Pegmatite

The specimen, with its combination of coarse and fine-grained crystals, is a modest example of the common coexistence or mingling of both very fine-grained and very coarse granitic lithologies. Such rocks typically form late in the evolution of a cooling mass of granitic magma, and the melt from which they crystallize is enriched in volatiles, such as H2O, CO2, F, Cl, and light elements such Li and B. All these components are significant in that they tend to lower the solidus of the melt, enabling magmatic-hydrothermal activity to continue to unusually low temperatures. F and B both cause great reductions in the granite solidus (Manning and Pichavant, 1983, 1988). Subsolvus granites may form late, with two feldspars, indicate of higher pH2O. A late water influx may induce fusion and remobilisation in a cooling hypersolvus granite (at lower temperatures deuteric changes would result: Martin and Bonin, 1976). Time is the key overall factor in crystal growth, combined with continued availability of the "nutrients" (such as boron for tourmaline) required for the mineral in question. For reviews of zoned pegmatites, including those in southern California, see Jahns (1982) and especially London (2008).

References (n=21)

Anon (2007) Meldon aplite quarry. Educational Register of Geological Sites, 18pp.

Barlow,FJ, Jones,RW and LaBerge,GL (editors) (1996) The F. John Barlow Mineral Collection. Sanco Publishing, Appleton, WI, 408pp.

Cassedanne,J and Cassedanne,J (1981) The Urubu pegmatite and vicinity. Mineral.Record 12, 73-77.

Dearman,WR (1962) Dartmoor, the North-West Margin and other Selected areas. Geologists' Association Guide 33, 29pp.

Drysdale,DJ (1985) Petalite and spodumene in the Meldon aplite, Devon. Mineral.Mag. 49, 758-759.

Falster,AU, Jarnot,MD, Neumeier,GA, Simmons,WB and Staebler,GA (editors) (2002) Tourmaline. Lapis International, 106pp.

Henderson,CMB, Martin,JS and Mason,RA (1989) Compositional relations in Li-micas from S.W. England and France: an ion- and electron- microprobe study. Mineral.Mag. 53, 427-449.

Jacobson,MI (2017) The early history of the Himalaya pegmatite mine, San Diego county, California. Mineral News, 8-12,14-15, January.

Jahns,RH (1982) Internal evolution of pegmatite bodies. In `Granitic Pegmatites in Science and Industry' (Cerny,P editor), MAC Short Course Handbook 8, 555pp., 293-327.

London,D (2008) Pegmatites. Canadian Mineralogist Spec.Publ. 10, 347pp. + CD-ROM.

Manning,DAC and Pichavant,M (1983) The role of fluorine and boron in the generation of granitic melts. In `Migmatites, Melting and Metamorphism' (Atherton,MP and Gribble,CD, editors), Shiva Publishing Ltd, Nantwich, 326pp., 94-109.

Manning,DAC and Pichavant,M (1988) Volatiles and their bearing on the behaviour of metals in granitic systems. In `Recent Advances in the Geology of Granite-Related Mineral Deposits' (Taylor,RP and Strong,DF editors), CIMM Spec.Vol. 39, 445pp., 13-24.

Martin,RF and Bonin,B (1976) Water and magma genesis: the association hypersolvus granite - subsolvus granite. Can.Mineral. 14, 228-237.

Mauthner,M (2015) The World of Tourmaline: the Gerhard Wagner Collection / Die Welt des Turmalin, die Gerhard Wagner Sammlung. Ivy Press, Inc., Dallas, TX, 264pp. (in Engl. and in Ger.).

McLintock,WFP (1923) On the occurrence of petalite and pneumatolytic apatite in the Meldon aplite, Okehampton, Devonshire. Mineral.Mag. 20, 140-150.

Quensel,P and Gabrielson,O (1939) Minerals of the Varutrask Pegmatite 14: the tourmaline group. Geologiska Foreningens Forhandlingar 61, 63-90.

Swoboda,ER (2002) History of the Tourmaline Queen mine, San Diego county, California. Mineral.Record 33, 409-425.

Webber,KL, Falster,AU, Simmons,WB and Foord,EE (1997) The role of diffusion-controlled oscillatory nucleation in the formation of line rock in pegmatite-aplite dikes. J.Petrol. 38, 1777-1791.

Wilson,GC (1980) Ion Microprobe Techniques, with Applications to Analysis of Lithium in Cornish Granites. PhD Thesis, University of Cambridge, 245pp.

Wilson,WE (2007) John Greiger and Thomas Warner: California mineral dealers and collectors. Mineral.Record 38, 463-471.

Wilson,WE (editor) (2014) Mineral Collections in Texas. Mineral.Record 45 no.5, supplement, 304pp., September.

Graham Wilson, 30 March 2018 to 03 April 2018

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or the "Rock of the Month Index" (a few relevant examples appear below).

Classification of Sample Descriptions available on this Site

Class/Group/Family Topics
The "Rock of the Month"with select "Museum Moments" (MM)
Borosilicates - B --- #120 --- Tourmalinite from Botallack, Cornwall, England
Borosilicates - B --- #100 --- Pegmatitic granite, Tregonning-Godolphin stock, Cornwall, England
Borosilicates - B --- #101 --- Tourmaline-rich granitic breccia, Wheal Remfry, Cornwall, England
Phyllosilicates - micas - Li --- #66 --- Lepidolite, Harding pegmatite, New Mexico