LABRADORITE

A silicate of aluminium, calcium and sodium which usually appears in an array of colours including blue, green, orange, red or yellow. Although it is colourless, its complex physical structure enables it to reflect and disperse light in an unusual way resulting in the visible rainbow effect. It is moderately hard (6-6.5 on the mohs scale) and has perfect cleavage.

It has an unusual glassy sheen known as schiller (the German word for iridescence) which makes it very valuable. Schillers result when light passing thorough the mineral bounces off inclusions. Schillers of labradorite are unlike schillers of any other mineral because they result when light bounces off particles of magnetite within the gemstone to produce a beautiful array of colours. This unique effect is known as labradorescence.

Labradorite is a plagioclase feldspar. Members of this group of minerals may often only be differentiated by the amount of calcium and sodium they contain and have been categorized into the plagioclase series. Albite, which contains mainly sodium and anorthphite, which contains mainly calcium lie at either end of the scale. Labradorite lies almost in the middle as it contains roughly equal quantities of both elements. It can be differentiated from other plagioclase feldspars due to its beautiful colours.

It is sometimes used for ornaments although care must be taken when cutting in order to prevent a reduction of the play of light.

It forms in igneous and metamorphic rocks often in association with deposits of andesite, basalt or gabbro. It was first discovered in the Labrador region of NE Canada in the late 18th century which is where it gets its name. It is still found in its original location today as well as in New South Wales Australia, Finland, Madagascar, Norway and around Mount Etna, Sicily.

LACE AGATE

A form of agate which is usually light blue and white and may be classified as a silicate or an oxide. Agate is an impure form of chalcedony which is a variety of quartz. Agates are distinguished from chalcedony by their surface banding which results from the presence of various impurities within them. Attractive surface patterns are evident due to microcrystalline inclusions of quartz which form in threadlike bands. Therefore the inclusions are made of the same components as the host material.

It is relatively hard (6.5 on the mohs scale) and may be used for ornaments or jewellery. It is fairly uncommon, which increases its commercial value.

It occurs mainly in rounded nodules of volcanic lava such as basalt (geodes). When the nodules are split open they reveal a banded zone of lace agate.

The most famous source is at Idar-Oberstein Germany where specimens have been collected since the 1500s. This source is now exhausted but the town is still remains the worlds leading centre for polishing and carving lace agate ornaments. Most lace agate is imported from Brazil and Uruguay. It can also be found in China, Egypt, Italy, Madagascar, Mexico.