166 THE MINERALS OF TASMANIA. 



belong to o, here taken as the positive tetrahedron ; they 

 are slightly striated parallel to their intersections with m. 

 The faces of a, o, m are bright, of d less so ; q is mostly 

 dull." 



These beautiful and interesting examples of crystalliza^ 

 tion occur in small vughs implanted on crystalline siderite, 

 associated with steinmannite and yellow translucent crys- 

 tals of sphalerite of the normal character. They are of 

 extreme rarity and exquisite development, although usually 

 small in size. 



304. Sphene (Titanate and Silicate of Calcium). 



This mineral is also known' as titanite. It is an abundant 

 accessory in various igneous rocks, and is of some petro- 

 graphical importance, and of interest to the mineralogist, 

 when in macroscopical crystals. The large crystals have 

 been used as gems, after passing through the lapidary's 

 hands ; but that is quite exceptional. It occurs frequently 

 in small, dark-yellow to brown, ill-formed tabular crystals 

 of resinous lustre in the amphibolite of Mt. Ramsay ; 

 generally in specimens showing both scheelite and ilmenite. 

 At first glance it might be mistaken for the much rarer 

 axinite, but on trial before the blowpipe it imparts no 

 colour to the flame, and the microcosmic salt bead light- 

 yellow in the oxidation flame turns to the — for titanic 

 oxide — characteristic violet colour in the reduction flame. 

 In small wedge-shaped crystals in the alkali and elaeolite 

 syenite of the Port Cygnet complex ; abundant as micro- 

 scopic crystals and particles in hornblende granite from 

 the vicinity of the Heazlewood River ; common accessory 

 ingredient in the rock from the Parson's Hood Mountain. 



This mineral decomposes to a white, earthy titanite, 

 which is known as leucoxene, and is abundant in micro - 

 sections of many igneous rocks. 



305. Spinel Black. (See Pleonaste.) 



306. Spherosiderite (Carbonate of Iron). 



This form of iron carbonate is peculiar to amygdaloidal 

 basalt, in which it occurs in globular concretions of vari- 

 able size; it is usually solid, but may be in tiers or scales, 

 with an invariable fibrous structure. It is in various 

 shades of brown, from pale to dark. As occurring in this 

 State it rarely exceeds an inch in diameter of the globules. 

 It is commonly mistaken for a form of zeolite, or even for 

 ferrocalcite, to which latter it is closely allied. It is 



