![]() The new material maintains the fibrous structure and appearance of crocidolite but now has the physical and optical properties of quartz such as an elevated hardness and a vitreous lustre. Tiger’s eye is produced when quartz replaces the internal composition of blue crocidolite asbestos.While its structure still resembles a piece of wood its other properties such as its density (now 2.60 to 2.65 instead of 1.00) and lustre (now vitreous) have been altered due to the internal replacement. For example silicified wood where ancient wood has had its composition replaced by quartz. The combination of quartz properties and other shapes can produce some interesting and attractive results. The new material is quartz and has all the same properties as other varieties of quartz except that it has taken on the shape of the previous material. Pseudomorph quartz - These varieties occur when quartz replaces another material and adopts the external form (habit) of that original material.A lot of the ‘onyx’ on the market is in fact chalcedony that has been dyed black. Brown and white banded material is called sardonyx. Onyx generally shows white and black bands however it can show other colours. The bands in onyx are straight and parallel unlike the curved bands of agate. However the name onyx technically refers to colour banded polycrystalline quartz. Onyx is a term used commercially to describe any black chalcedony.Blue-lace agate is pale blue with delicate (lace-like) white banding.Moss agate contains dark green dendritic mineral inclusions that resemble branches or mossy growth.Fire agate displays a play of colour or iridescence effect due to the presence of thin layers of platy minerals between the layers of chalcedony. ![]() It is relatively easy to alter the colour of agate with dye and that is why, commercially, agates can be found in all imaginable colours. Some agates have been given particular names usually related to their unique appearances. The different layers can be different colours or simply different shades of the same colour.
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