Peter Rosewarne

And now for something completely different, from me at least. I don’t normally write about semi-precious ornamental stones/rocks but felt there was a story in this one based on a long-ago overseas trip, a more recent article in the Mineralogical Record, some carvings I have from the former and some mineral specimens related to the latter.

Firstly, some technical clarity about lapis lazuli, or ‘lapis’, which many of you probably don’t need. I had always thought that it was a mineral in its own right but on reading up on some background material find that it is a rock type rather than a mineral and that it is in fact made up of a number of minerals, chief among them being lazurite (Na6Ca2[Al6Si6O24]S2), then calcite, wollastonite, nosean, haϋyne, pyrite and diopside, in varying proportions, and some other mostly trace minerals that do not influence its appearance. Lazurite is a feldspathoid, which is basically a silica under-saturated feldspar. Nosean and haϋyne are also feldspathoids and form part of the Sodalite Group. The blue colour of lazurite is due to its sulphur content and the deeper the blue the better the grade and desirability of the lapis.

There are two commercially viable deposits of lapis being worked in the world, one in Afghanistan (east) and one in Chile (west), hence the title of this article. Other non-commercial deposits are found in Russia near Lake Baikal, the USA, Canada and Italy. Both the ‘east’ and ‘west’ deposits occur in mountainous terrain, the former in the Hindu Kush and the latter in the Andes.

East: Afghan Lapis

This site is located in the northeast of Afghanistan at an altitude of c.2 725 m in the Hindu Kush (Figure 1), has been known and worked for at least nine thousand years and is the world’s oldest still active mining district. It consists of a series of workings (Figure 2) dug into high-grade metamorphic rocks and known as Sar-e-Sang, after the name of the local ‘river’ and miners’ settlement.


Figure 1


Figure 2

(Figures 1 and 2 reproduced with kind permission from the Mineralogical Record).

Apart from ornamental-grade lapis this is the world’s only site that produces fine crystals of lazurite and also world-class crystals of sodalite, afghanite and haϋyne, amongst others. The deposits are hosted in marble enriched in calcium and magnesium silicates and carbonates, sometimes referred to as a calciphyre but more commonly known as a skarn. Figure 3 shows a slab of lapis 15 x 4,5 x 2 cm showing its deep blue colouring because of minimal accessory minerals, with only speckles and very thin veinlets of pyrite and white and grey minerals/marble. I bought this from Earthstone, Fire and Ice at Monte Casino in Johannesburg, not in Afghanistan, although most of this lapis is reportedly sold in Peshawar in Pakistan.


Figure 3

I have a couple of crystal specimens of lazurite from this locality obtained from internet dealers, which are shown in Figures 4 and 5. Figure 4 shows a 2 cm euhedral crystal protruding from white marble with pyrite veining, while Figure 5 shows a crystal aggregate with diopside and pyrite veining.


Figure 4 with 2 cm crystal


Figure 5 FOV 6 cm

Afghan lapis was apparently used in the exquisite pietra dura (marble inlay work) decoration of the Taj Mahal. I visited this iconic site in 2019 but the photos I took of this inlay work didn’t include lapis. However, Agra is also famous for artisans who produce intricately inlaid table tops, boxes and the like using white marble from Rajasthan inlaid with paper-thin semi-precious stones. Figure 6 shows the top of a box I bought for my wife, after falling for a bit of a tourist-sucker visit to a local factory in Agra, showing lapis plus, I think, carnelian, malachite, onyx and mother of pearl.

Figure 6

West: Chilean Lapis

 In 1994 I did a trip to Chile to investigate a proposed copper mine, Collahuasi (pronounced kyawasi if I recall correctly), at an altitude of 4 500 m in the Andes near the border with Bolivia. This is a spectacular setting, and at that altitude, literally breath-taking(!), with mountains, smoking volcanoes, one with a sulphur mine at the top, and white salt lakes or salars as they are called locally. It is now the second largest copper mine in Chile and the third largest in the world. I was investigating groundwater issues, mainly related to groundwater pressures on pit slope stability and design. A scenic ‘file’ photograph of the mine and general area is shown in Figure 7 (approximately around C on Figure 8). However, I digress...



Figure 7


Figure 8

Head office of the exploration company was located in the capital, Santiago, a very pleasant city with wonderful draft beer, or shop, a drink called pisco sour (a heady concoction of the local spirit pisco, lime juice, beaten egg white and sugar; a couple of those before heading out in the evening certainly brightened one’s outlook!) and beautiful women, but again I digress. I did some touristy things during time off, apart from drinking beer, and bought some attractive lapis carvings.

The source deposit is located in the Coquimbo District, about 400 km north of Santiago (approximately L on Figure 8 above: It’s a funny looking map but Chile is a looooong country) at an altitude of c.3 500 m in the Andes mountains. The deposit has been mined since 1905 and is hosted in contact-metamorphosed limestone that was later metasomatised by the introduction of sulphur, a necessary ingredient for the formation of lazurite. The Chilean lapis tends to have more white and grey streaking and less pyrite than the Afghan lapis. It is all of a massive nature with no crystals being present, as far as I can ascertain.

Figures 9 and 10 below show examples of the carvings I bought in Santiago. Figure 9 shows detail from the lid of a jar (7,5 cm diameter) and an egg, and illustrates the streaky nature of much of this lapis. Figure 10 is a miniature replica (12,5 cm tall) of one of the famous Easter Island statues and a lion (wrong species for Chile though). However, the real statues, locally called moai, are carved from volcanic tuff, not lapis! One of them is on display outside the Fonck Museum in Valparaiso, a coastal city about 120 km west of Santiago, as shown in Figure 11. It was mounted there in 1950 and is apparently one of only six such statues existing outside of the island.




Figures 9, 10 and 11

Thanks for joining me on this brief east vs west look at lapis lazuli. As with all these articles, I’ve learned something new and I hope you have too. Until the next one…

References

Bernard J.H.  and Hyrsl, J. (2006), Minerals and their Localities. Granit.

Coenraads, R.R. and Canut de Bon, C. (2000), Lapis Lazuli from the Coquimbo Region, Chile. Gems and Gemology. Spring 2000.

Mineralogical Record (2014), SAR-E-SANG. May-June 2014, Vol. 45, No. 3.

Rough Guides. The Rough Guide Map: Chile 1:1 600 000. Penguin.

Schumann, W. (2000) Gemstones of the World. Revised and expanded edition. N.A.G.Press.

Thomas, A. (2008), Gemstones: Properties, identification and use. New Holland Publishers.