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Students examining large spodumene crystals in the Etta mine, South Dakota

Photo Source : Unknown

Giant Spodumene "Logs" in the Etta Mine, Black Hills, Pennington County, South Dakota, USA

Coordinates : 43°52'N , 103°25'W : Etta mine, Keystone, Pennington Co., South Dakota, USA

To see the Etta Mine on Google Earth, please click here.


- Giant Spodumene "Logs" in the Black Hills -


The Etta mine near Keystone in the Black Hills began operations in 1883 as a mica mine. Accompanying "black ore" turned out to be rich tin ore, triggering a tin rush in the surrounding Black Hills, which resulted in the claiming of several other mines in the vicinity. However no substantial tin ore bodies were discovered and most mines were abandoned soon. In the Etta however the tin boom at least proved the existence of large quantities of lithium ores in form of large spodumene crystals, which were mined separately since 1898.

The Etta mine operated until 1959. It became famous for its giant spodumene crystals, which form individual "crystal logs" in a quartz - feldspar - mica matrix. These spodumene logs reached remarkable dimensions, whereas the first reference of the logs at the Etta mine was by Blake in 1883. A detailed survey of the mineralogy of the Etta Mine has been done by Frank Hess in 1939. He wrote :

'Huge crystals of spodumene are mixed at every possible angle like toothpicks in a translucent gel (quartz). In 1904, a crystal 42 feet long and 3 feet by 6 feet in cross section was found...The crystal weighed about 65 tons.'

Spodumene crystals of similar dimension were abundantly found in the course of lithium exploitation at Etta. Giant Spodumene crystals of up to 10 m = 30 feet were discovered also in the nearby Ingersoll mine, accompanied by large orhoclase and beryl crystals as well as at the Tin Mountain Quarry

Today the abandoned Etta mine, with its gaping open pit, is still a spectacular sight and large spodumene crystals can be spotted at the steep rock walls. However the mine is on private property and visitors are generally not greeted with a warm welcome. Though this may change, as the Etta mine was up for sale recently.

The Etta mine in a Nutshell :

Mineralogy :

Spodumene, accompanying minerals are amblygonite, feldspar, quartz, mica and cassiterite

Maximum Crystal Size :

Spodumene crystal "logs" up to 14 meter size, and meter - sized feldspar crystals

Geology & Formation :

Lithium and beryl rich pegmatites, direct crystallization from granitic melt

Current status :

Inactive, partly flooded mine on private property

Remarks :

A classic locality of giant crystals, now largely mined out. However, spodumene logs of considerable size can still be observed in the walls of the open mine pit



Resources and Relevant Weblinks :

For more information on the mineral spodumene please look at, Webmineral and the german Mineralienatlas.

- Another locality with giant spodumene crystals is the nearby Tin Mountain quarry, where a 10 m large spodumene crystal was discovered.

- A further well known north american spodumene locality is the Harding mine in New Mexico, where a multitude of up to 5 m long crisscrossing spodumene crystals in the pit walls are still acessible today. For more information click here.

- Gemmy spodumene of the pink variety known as kunzite can reach up to 1 m crystal size and is reported both from Brazil as well as from the Nuristan region, Pakistan

The Etta mine and many other pegmatite mines in the Black Hills have raised geological interest since a long time and today they constitute one of the classic geological field trip areas for many geological departments in the US. Therefore there is a vast literature available about this area, which is probably one of the best documented 'giant crystal areas' worldwide.

To name a few :

Blake, W. P. (1884) Transactions of the American Institute of Mining Engineers Vol. XIII: “Tin Ore Veins of the Black Hills”.

DeWitt, E., Redden, J. A., Burack Wilson, A., and Buscher, D. (1986) Mineral resource and geology of the Black Hills National Forest, South Dakota and Wyoming. United States Geological Survey Bull. 1580 

Guiteras, J. R. (1940) Mining of feldspar and associated minerals in the southern Black Hills of South Dakota. United States Department of Interior, Bureau of Mines, IC 7112. 

Hess, F. L. (1939) Lithium. United States Department of Interior, Bureau of Mines, IC 7054 

Landes, K. L. (1928) Sequence of Mineralization in the Keystone, South Dakota pegmatites. American Mineralogist v. 13, p. 519. 

Lincoln, F. C. (1927) Pegmatite mining in the Black Hills. Engineering and Mining Journal v. 123, n. 25. 

O’Harra, C. C. (1902) The mineral wealth of the Black Hills: South Dakota School of Mines Bull. 6 

Roberts, W. L., and G. Rapp Jr. (1965) Mineralogy of the Black Hills. South Dakota School of Mines bulletin 18.

Ziegler, V. (1914) The minerals of the Black Hills. South Dakota School of Mines bulletin 10.

Furthermore there is an excellent online publication on the subject : Black Hills Pegmatites !! by Thomas A. Loomis, published in : MATRIX Vol. 10, No. 3 Issue



Giant white spodumene logs in
the walls of the Etta open pit

Photo : A.V. Morgan

Cross section of the Etta Mine in 1929 clearly showing the large
spodumene "logs" in the main pegmatite body

Rendered by G.M. Schwartz and reproduced from Economic Geology, Vol. 20 (1925)

View into the partly flooded Etta open pit

Photo source : Gary Arndt at

Historic photo of two spodumene "logs" excavated around 1920

Photo source : United States Geological Survey



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