AMERICAN MUSEUM GUIDE LEAFLETS 
drawn to the beautifully developed hexagonal crystals and the rich and 
striking colors shown in this handsome suite of specimens. Among 
the rarer phosphates in Case 17 will be found many minerals which by 
reason of their beauty and interest will well repay a short inspection. 
Among these may be mentioned descloizite, the lead-zine vanadate; 
libethenite and pseudomalachite, the rare copper phosphates; roselite 
and erythrite, arsenates of cobalt, and variscite, a phosphate of 
aluminum. 
W avellite (Case 18), another phosphate of aluminum, presents many 
striking examples of radiating and stalactitic structure combined with 
colors of choice delicacy and attractiveness. Turquoise, the familiar 
gem mineral, here takes its place among the phosphates and is represented 
by a fine series of matrix specimens which illustrates its distribution as 
well as its slight color variations. The radioactive minerals torbanite, 
copper uranium phosphate, and autunite, the calcium uranium phos- 
phate, are represented by many specimens, which in the instance of 
autunite give evidence to the unaided eye, by the singular quality of 
their yellow green color, of the unusual character of their emanations. 
Among the borates in Case 18 will be found a remarkably hand- 
some and complete suite of colemanite, a calcium borate from California. 
Case 18 also contains the radium minerals uraninite, gummite and 
carnotite. Of these, uraninite contains the higher percentage of radium, 
but carnotite, owing to its wider distribution in the Western United 
States, is becoming the more important radium ore. 
SULPHATES 
Cases 18, 19, K and 20 
Like the phosphates, the minerals of the Sulphate Division are 
mostly secondary products which have been derived from other minerals 
or rocks by alteration. The action of water upon most of the sul- 
phides of the metals produces from these sulphuric acid and metallic 
oxides, which combine to form sulphates. Many of these sulphates 
are soluble in water and are consequently carried away in solution to 
be deposited elsewhere, but the larger number of them are to be found 
in more or less close proximity to the primary minerals from which they 
were derived. 
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