Curling Stones

August 24, 2017

Lesley Andrews gave a most interesting talk on Scottish curling stones. I thought curling was a Scottish winter game played by village yokels. I was wrong! It has had Winter Olympic status since 1998. The game consists of two teams of four players each, with eight stones between them, and the idea is to slide the stone, which turns, hence the name curling, towards a target called a button. Rather like a game of bowls on ice. The origin of the game goes back into obscurity, but the oldest known curling stone is dated back to 1510. The stone is quarried from the island of Ailsa Craig, just off the southern coast of Ayrshire in the Firth of Clyde in western Scotland. The stone is ferried across to the harbour of Girvan, and taken to the factory at Mauchline, inland.

Sitting in the Firth of Clyde the profile of Ailsa Craig is easily recognised when viewed from the Ayrshire coast. Approximately 10 miles from Girvan it is nearly two miles in circumference and rises to 338 m. The island was formed as a result of intense volcanic activity 60 million years ago.


The island is geologically interesting, having a pale, greenish microgranite called “ailsite”, from which the curling stones are made. There are prominent jointed columns, of what seem to be dolerite sills on the island which is about 1,3 km across. The stone has been quarried from about 1750. It contains quartz, Na and K feldspars, riebeckite, aegerine, and aenigmatite. No micas, sulphides or clay minerals are present, making the rock tough and compact.

The rock is lathe-turned into a large bun-shaped curling stone, weighing 17–20 kg. A coloured, durable plastic handle is attached to each stone. The stones are highly polished, with an “equator” band sand-blasted onto the stone, called the striking band, to knock other stones out of the way when skimmed along an icy surface. There is also a narrow running band made from an insert of Blue Hone granite (also from the island) on the bottom of the stone where it touches the ice. There are fears about the future of the Ailsa Craig quarries, as no more blasting can take place because the island has been declared a sea bird nature reserve since 2004. Loose rock can still be collected. Welsh Trefor granite, or some other similar igneous rock may have to be used in the future. Experiments are afoot about using a porcelain ceramic, called “ailset” after the island. Lesley brought a selection of souvenirs made from the Ailsa Craig microgranite, including miniature curling stones, earrings, and “ice blocks” – you put the ice blocks in the freezer to get cold and pop them in a glass of your favourite blend of whisky which then doesn’t get diluted, as it does by normal ice.

The talk was illustrated by a slide show and video clips. These ended with an amusing, kitch, architectural masterpiece of a pizza outlet somewhere in Canada, built to resemble a giant curling stone. I think all who attended this meeting found Lesley’s talk fascinating. I hate games of all kinds, but I thoroughly enjoyed every moment of the talk, including clips of seeing the game played. It was a great meeting. TVJ

Credits: The Ailsa Craig photo is by Davie Law, 2005, and the curling stone one is from a Kays of Scotland website.

 If you wish to learn more about curling, try the website   www.worldcurling.org.

 

FACETING FOR INCLUSIONS

July 24, 2017

Duncan Miller

Inclusions in gemstones often are seen as just a nuisance by faceters, who find themselves urged to buy only ‘clean’ rough. I suppose it is a matter of taste, but inclusions that do not detract from the visual appearance of a gemstone can aid in proving its authenticity. And some inclusions definitely enhance the value and appearance of certain gems. A visible ‘horse tail’ inclusion of asbestos fibres in Russian demantoid is perhaps the most famous example of desirable ...


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Synthetics

June 27, 2017

Duncan Miller

Synthetics are a wonderful source of relatively inexpensive faceting rough, in a wide array of colours, some of them not available at all in natural stones. On the whole, synthetic gem rough is predictable in its behaviour and also enables the cutter to explore quirky cuts in larger sizes than would be affordable in natural rough. And increasingly jewellers are setting well-cut synthetics in precious metal jewellery. So dive in, and enjoy yourself.

The most commonly available ...


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New Barite Occurrence at Rosh Pinah Mine – Namibia

May 23, 2017

Transparent to whitish barite mineralization was found in an orogenic late phase leached fault zone. It seems that some of the barites are pseudomorphs replaced by snow white baritocalcite. This replacement supposedly took place at an even later phase when calcium-rich fluids migrated through the formation. This theory is supported by the occurrence of floater quartz crystals in a pocket where, on the one side, the quartz aggregates display the luster of ‘bergkristall’ and are coated on t...


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The History behind the Mike Lurie Collection

May 23, 2017

The Lurie family lived in Bulawayo, Rhodesia/Zimbabwe, from 1951 to 1966. During this time Robert’s late father, Mike, worked as a manufacturer’s representative. His job took him by car all over Southern Rhodesia (Zimbabwe), Northern Rhodesia (Zambia) and Nyasaland (Malawi). Every now and again Mike would stop his car in the middle of the bush to take a break from the difficult, long distance driving. He would often notice something shining, or an agat...


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Working With Diamond

May 23, 2017

Duncan Miller

No, this is not about polishing diamonds, which in South Africa is illegal without a license, but about working with diamond grit or paste. For the coloured stone gem cutter, diamond paste is easier to source and to use. Loose grit and pastes are available in a range of mesh sizes, with crushed natural diamond or synthetic diamond. Synthetic diamond is made as single crystals and polycrystalline aggregates. The polycrystalline diamond breaks down with use to produce finer parti...


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TOURMALINE

April 25, 2017

Duncan Miller

Tourmaline can be temperamental. Rough tourmaline occurs in two distinct shapes – globular nodules and elongated pencil-like crystals elongated in the direction of the c-axis. The globular nodules sometimes spall concentrically, like onions, and the pencils sometime fracture transversely. This behaviour is difficult, if not impossible to predict, although fine cracks in the ‘skin’ of tourmaline pencils is not a good sign. The cracked skin must be removed by preforming or th...


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New Barite Occurrence at Rosh Pinah Mine – Namibia

March 25, 2017

Author: Gisela Hinder, Rosh Pinah Geo Center, Rosh Pinah, Namibia

e-mail: gisela.hinder007@gmail.com

 Rosh Pinah Mine is situated in the southwest of Namibia about 80 km east of Oranjemund. Rosh Pinah Mine became well known for its beautiful barites when a massive pocket of yellow to orange barite crystals was opened in 1989. It is said that these barites were the best ever found in Namibia.

In February 2017 new barite crystals were discovered at Rosh Pinah. Yellowish, unfortunately smallish, ...


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GARNET

March 25, 2017

Duncan Miller

Garnets are among the easiest gem materials to facet. They have no distinct cleavage, although some crystals have a parting that causes them to fracture into thin slabs. The rough often is in globular shapes, which is good for weight recovery. When choosing rough, avoid being fooled by fake material. Red glass is sometimes covered in adhering deceptive ‘grit’ to mimic natural nodules. Illuminated from behind or the side with a torch, the characteristic internal swirls and r...


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A Bit about Blue Lace Chalcedony

March 25, 2017

Jo Wicht

Blue Lace “Agate” is found on the farm Ysterputs 254 (meaning iron holes) in Namibia. The mine is located adjacent to the “Blinkpan” (shining shallow lake) which can be seen to the west of the B1 highway about 80 km north of Vioolsdrift and Noordoewer, which are the border towns on either side of the Orange River between South African and Namibia.

Blue lace is not a true agate, but a chalcedony (microcrystalline quartz) laid down in a series of wavy bands, which gives it th...


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