418 SYSTEMATIC DESCRIPTION OF PRECIOUS STONES 



comparatively rich in iron, ranges from 3-47 to 3-5 ; these therefore sink in pure methylene 

 iodide, but float in the heaviest liquid (sp. gr. = 3-6). Epidote is fusible before the 

 blowpipe, and the fused mass is decomposed by acids ; fresh, unfused material, however, is 

 not attacked by acids. 



Epidote of almost all degrees of transparency is to be met with, but perfectly transparent 

 crystals of a dark colour are rare, except at the Knappenwand. Both the refraction and 

 the double refraction are strong. The range of colour is somewhat extensive ; it depends 

 upon the presence of iron, and the larger the amount of iron present the deeper the colour of 

 the stone. Almost colourless crystals are rarely met with, pale yellow and red stones are 

 more frequent, but the colours most commonly seen are more or less dark shades of 

 pistachio-green. This colour, which may be described as a dark green with tones of 

 yellow and brown, is so characteristic of epidote that this mineral is sometimes referred 

 to as pistacite. This dark pistachio-green colour may be seen in Fig. 1 of Plate XIV., 

 which represents a druse of crystals from the Knappenwand, while Fig. 2 of the same 

 plate represents a cut stone. In reflected hght the Knappenwand epidote appears dark 

 green or, in thick crystals, almost black in colour. The light which is transmitted through 

 the prism in a certain direction is, however, of a bright green colour, while that which 

 travels in a direction perpendicular to this is yeUowish-brown, sometimes tinged with red. 

 Epidote is one of the most prominently dichroic of minerals ; the images seen in the 

 dichroscope vary between green, yellow, and very dark brown. 



The stone is cut in the forms usually employed for other darkly coloured stones, 

 namely, in low step-cuts and table-cuts (Plate XIV., Fig. 2). Cut stones must not be too 

 thick, otherwise the colour will be dark and unpleasing ; it is sometimes improved, however,, 

 by placing a burnished foil beneath the stone. According to the orientation of the large 

 front facet or table with respect to the crystal the stone will appear more green or more 

 brown in colour. The lustre of cut stones is vitreous in character and very brilliant. 



Epidote is easily distinguished from other green and brown stones by its strong 

 dichroism and high specific gravity. Greea and brown tourmaline, which is also strongly 

 dichroic, is much less dense (sp. gr. = 3-0 - 3-1) ; it therefore floats in pure methylene 

 iodide. Diopside, chrysolite, and other green stones which might possibly be confused with 

 epidote are all much more feebly dichroic, and the same is true of smoky-quartz. The 

 confusion of epidote with brown stones, however, is not very likely to occur, since the . 

 former is usually cut in such a manner as to display its green and not its brown 

 colour. 



This mineral is generally found in ancient silicate-rocks ; the crystals occur either 

 completely embedded or attached to the walls of cavities. At the Knappenwand, in 

 the Untersulzbachthal, Salzburg, crystals occur attached to the walls of crevices in massive 

 epidote, the so-called epidote-schist ; the exact spot is below the Poberg ridge, and was 

 discovered in 1866. Here are found by far the most magnificent crystals of epidote 

 known, and the locality affords one of the most beautiful examples of the occurrence of 

 minerals. Thousands of crystals have been found there, many of which are distributed 

 throughout the mineral collections of the world, while others have been cut as gems. Some 

 are of considerable size, as much as 45 centimetres in length and 3 to 4 centimetres in 

 thickness, but most are much smaller. In association with the epidote are to be found 

 crystals of calcite, apatite, felspar, and certain rare minerals ; also fibres of asbestos, which 

 sometimes form a thick felted mass round the point of attachment of the epidote prisms, 

 as may be distinctly seen in Plate XIV., Fig. 1. 



Epidote is found at many other places in Europe, but nowhere in crystals of such. 



