PRECIOUS STONES. 9? 



ious colours). H. 7'6. Very dichroic. 

 ish-green variety of olivine. Chrysolite, a yellow 

 or gxee^wghjjDelWw variety, is softer than quartz. 



Zircon (including hyacinth and jargoon) is of various colours. S.G-., 

 4 7 , and thus the heaviest of precious stones . H. 7 ' 5 . Crystallization , 

 tetragonal. 



Moonstone, sunstone (with internal reflections), and adularia are 

 varieties of felspar. 



Lapis-lazuli is a nearly opaque, blue stone. (H. 5'2.) 



Smoky quartz, cairngorm, false topaz, milky quartz, yellow or 

 citron quartz, rose quartz, rock crystals, Bristol and Gibraltar 

 diamonds, are varieties of quartz ; so too are crocidolite, onyx, 

 sardonyx, sard, bloodstone, jasper, agate, moss agate, or mocha stone. 

 chrysoprase (of an apple-green colour), plasma (green), chalcedony, 

 cornelian, avanturine (usually brownish or greenish, speckled with 

 mica), heliotrope (spotted), firestoneand quartz cat's eye, potato-stone, 

 &c. 



The crystallized varieties are usually of the form of hexagonal 

 prisms capped by pyramids, and have approximately S.G. 2 - 65 ; 



Jade (generally slightly translucent and greenish, greenish white, 

 milky white, &c., includes N.Z. greenstone. H. 6'5 to 7). 

 Alexandrite and oriental chrysolite are varieties of chrysoberyl. 



There are many of the gems of comparatively little 

 value that are in reality not always profitable for a person 

 to pay much attention to the discovery of; that is, of 

 course, unless the quantity of them is great, for the cost 

 of polishing the same is an important factor in assigning a 

 value to them. Many coloured transparent and translucent 

 kinds of quartz, coloured by metallic oxides, fall under this 

 category. But so easy is it to prospect a stream, say in 

 a country of crystalline, plutonic, or metamorphic rocks, 

 that a search for precious stones and gems of all kinds 

 should be made much more than is usually the case. With 

 regard to the precious varieties, it is well to bear in mind 

 for instance, when dealing with a heap of Ceylon gem 

 stones that the valuable specimens may be associated with 

 all sorts of worthless specimens, all of whidh, though impure 

 in quality, may really be sapphires, spinels, chrysoberyls, 

 tourmalines, zircons, &c. 



Though many are translucent rather than transparent, 

 many dark in outward appearance, and all water-worn, 

 more or less, and with surfaces not at all glass-like, and 

 the majority not apparently transparent or translucent un- 



