BLUE AND BLACK SPINEL 299 



rivers of New South Wales ; also in Victoria, for example in Owen's river, and in other 

 States. Single stones have been found also in Tasmania. 



The so-called " vinegar-spinel " has already been stated to occur in the gem-gravels 

 of Minas Novas, in Brazil. In the United States of North America, a few spinels 

 suitable for cutting, although rather dark in colour, have been found at Hamburgh 

 in New Jersey. The sapphires of Montana are remarkable in that they are not 

 accompanied by spinels. Other localities for spinel are of even less importance and need 

 not detain us. 



Blue Spinel. — Among the colours of spinel, blue is not very prominent ; stones of 

 this colour exist, however, and may be referred to as " sapphire-spinels" in correspondence 

 with the term " ruby-spinel ■" applied to stones of a ruby-red colour. The colour of these 

 stones is due to a small amount of ferrous oxide in combination with alumina, which is 

 present in addition to magnesia. Blue spinel occurs, often in large crystals, at Aker in 

 Sodermanland, Sweden ; at this locality, however, the mineral is often opaque and scarcely 

 of gem-quality. Transparent stones occur as isolated specimens, together with red spinel, 

 at the localities mentioned above, that is to say, in Burma and especially in Ceylon. In 

 the latter island are found very beautiful, dark blue octahedra. The lustre of these 

 stones when cut as gems, although inferior to that of sapphire, is still very brilliant. 

 In beauty of appearance they do not fall far short of sapphires, and they command a 

 good price. 



Black Spinel (ceylonite or pleonaste). — In this variety of spinel a part of the 

 alumina is replaced by ferric oxide and the greater part of the magnesia by ferrous oxide, 

 so that instead of a magnesia-alumina spinel, we get an iron-alumina spinel, the chemical 

 composition of which may be represented by the formula (Mg,re)0.(A],Fe)20g. Being 

 only another variety of spinel, its crystalline form is the same as that already described for 

 precious spinel ; the combination shown in Fig. 60 b is, however, commoner in this variety 

 than in others. Ceylonite is greenish-black in mass and dark green in thin layers ; like all 

 spinels it takes a good polish and may be used in mourning jewellery. It is found in 

 loose grains, sometimes exceeding an inch in diameter, in the gem-gravels of Ceylon, 

 especially near Kandy ; also as small brilliant crystals in some of the ejected blocks of 

 Monte Somma, the ancient portion of Vesuvius. At many other localities it occurs as a 

 contact-mineral in limestones, which have been subjected to the action of masses of molten 

 granite and other igneous rockf. Large octahedra of black spinel, measuring 3 to 4 inches 

 along the axes of the crystals, are found at Amity in the State of New York ; small crystals 

 occur in great numbers in the i^'assathal in the Tyrol, and at many other places ; few, 

 however, are suitable for cutting. Green spinels, some of which are transparent and have 

 been used as gems, have been found in Mitchell County, North Carolina, and in a lead mine 

 in New Mexico. 



