Prismatic beryl specimens from China

--- at the Geological Museum of China and the China University of Geosciences- Beijing, China

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Figure 1. A beautiful specimen of coarse crystalline beryl. In each of the three samples shown here, the matrix appears to be a granitic pegmatite, a mixture of coarse, pale quartz and feldspars. At present, I do not know the exact location(s) of the material. Similar long, prismatic green beryl ("Malipo emeralds") are reported near the Vietnamese border in southwest Yunnan, near the border of China and Vietnam. One location is the Dayakou tungsten mine, 60 km south of Malipo in Wenshan prefecture.Beryl host rocks in the region include granite, pegmatite, mica schist and gneiss. The Dayakou (Dyakou) emerald occurrence lies in the north part of a 2,000 km2 metamorphic core complex (Xue et al., 2010). This sample was on display (2016) at the Geological Museum of China, in Beijing (next to Exit D (southwest) of the Xisi (line 4) subway station).


"Rock of the Month #186, posted for December 2016" ---

Coarse prisms of beryl

are featured this month. Here are photographs of three large specimens in two museums in Beijing. Each sample is circa 20-30 cm in height. Beryl is a famous gemstone, most notably as emerald, but other forms include morganite, aquamarine, heliodor, goshenite, and a caesium-rich blue beryl. Thus beryl, a cyclosilicate of the light element beryllium, is allochromatic, displaying a variety of colours, including greens to blue, pink and yellow. In this, it is similar to a more common prismatic cyclosilicate, tourmaline. Beryl is hexagonal, with a Mohs hardness of 8, and generally grows in hexagonal prisms, which may grow to many kilograms in weight. When not gemmy, beryl is the chief ore of the light element beryllium. A Be-Al silicate, pure beryl contains circa 14% BeO. The ideal formula is Be3Al2Si6O18.

Moore (2016, vol.1, pp.209-211) describes nine regions of China that produce notable beryl specimens. These are
  • Ailaoshan Mountains, Yunnan
  • Altay Mountains, Xinjiang
  • Dabdar, Taxkorgan region, Xinjiang
  • Dayakou mine, Yunnan
  • Gaoligongshan Mountains, Yunnan
  • Huanggang mine, Inner Mongolia
  • Pingjiang county, Hunan
  • Tongchang pegmatite, Hubei
  • Xuebaoding Mountain, Sichuan

Beryl is but one of many ornamental stones, gemstones and fossils that are revered in China (Chinese Red, 2012; Liu et al., 2013). Beijing is an excellent place to start exploring the geological diversity of this huge country. It includes the national geological museum (Bancroft et al., 1987) and other fine collections, as well as all manner of examples of uses of building stones, from ancient to modern.

Emerald deposits are widespread across the globe. Deposit settings include: 1) granite pegmatites and hydrothermal veins in mafic-ultramafic rocks; 2) thrusts and shear zones in mafic-ultramafic rocks; 3) oceanic suture zones; 4) thrusts and faults in "black shale" sediments; and 5) granite cupolas (Groat et al., 2007). Topaz may also be found in rhyolite flows and vugs therein, with notable occurrences (Wah Wah Mountains, Thomas Range) in the state of Utah, USA.

In China, beryl is found in pegmatites in Xinjiang, Hunan and Yunnan provinces, and elsewhere (Li et al., 1998, Lu and Wang, 1993). In north-central Sichuan province beryl and scheelite occur in vein deposits, as at Xuebaoding Mountain. Here beryl occurs as colourless goshenite, pale blue aquamarine and very rare pink morganite, with fluorapatite, euclase, cassiterite, muscovite, fluorite and scheelite (Ottens, 2005). Skarn minerals, including boron and beryllium species (beryl included) occur at the Huanggang mine in Inner Mongolia (Ottens and Neumeier, 2012).

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Figures 2-3. Here are two more superb specimens of beryl,
from the museum of the China University of Geosciences - Beijing,
as seen on display in 2016.


References

Bancroft,P, Zhengzhi,H and Furui,W (1987) The Peking geological museum, China. Mineral.Record 18, 325-332.

Chinese Red (2012) China Stones. Chinese Red, Beijing, 2012.2, 163pp. (in Engl. and in Ch.).

Groat,LA, Giuliani,G, Marshall,D and Turner,D (2007) Emerald. In `Geology of Gem Deposits' (Groat,LA editor), Mineral.Assoc.Canada Short Course 37, 270pp., 79-110.

Li,ZL, Zhang,WL and Yang,RY (1998) The analysis of chemical composition of melt inclusion of beryl in pegmatite and discovery of zinc spinel by electronic probe. Abs. International Mineralogical Association 17th General Meeting, 147, Toronto.

Liu,G, Lavinsky,RM, Meieran,ES, Schmitt,HH, Moore,TP and Wilson,WE (2013) Crystalline Treasures: the Mineral Heritage of China. Mineral.Record 44, supplement, 104pp.

Lu,H-Z and Wang,Z (1993) Mineralization, fluid and melt inclusions studies on No.3 pegmatite of Keketuohai, Xinjiang province, China. GAC/MAC Abstracts, 61, Edmonton.

Moore,TP (2016) Moore's Compendium of Mineral Discoveries, 1960-2015. Mineralogical Record, Inc., Tucson, 2 volumes, 809+813pp.

Ottens,B (2005) Xuebaoding, Pingwu county, Sichuan province, China. Mineral.Record 36, 45-57.

Ottens,B and Neumeier,G (2012) The Huanggang mine, Inner Mongolia, China. Mineral.Record 43, 529-563.

Xue,G, Marshall,D, Zhang,S, Ullrich,TD, Bishop,T, Groat,LA, Thorkelson,DJ, Giuliani,G and Fallick,AE (2010) Conditions for early Cretaceous emerald formation at Dyakou, China: fluid inclusion, Ar-Ar, and stable isotope studies. Econ.Geol. 105, 339-349.

Graham Wilson, 24,29,31 December 2016.

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