N ON -METALLIC MINERALS. 
Ill 
other phosphatic substances applied to similar purposes. In 
the lias, green-sand, and other secondary formations numerous 
coprolites and phosphatic nodules occur ; and in some of the 
Crags of our eastern counties they are also found, with various 
mammalian and other animal remains. By the action of sul- 
phuric acid these are converted into the soluble super-phosphate 
of lime, in which form they are largely employed for manure. 
Valuable phosphatic deposits are now worked in South Carolina 
and in Florida. 
An extensive series of phosphates, of economic value, is shown 
in the gallery of Model Room B. 
Case M. — Fluor-Spar. 
The species Fluor-spar is here represented by a number of 
specimens, not less attractive by their variety of colour than by 
their beauty of crystalline form. The mineral, which is a 
fluoride of calcium, is' found in nearly all our mining districts, 
especially in Cumberland and Derbyshire, Devon and Cornwall. 
It chief uses are as a flux in certain metallurgical operations, and 
as a source of hydrofluoric acid. 
The violet-blue variety of fluor, known commonly as “ Blue’ 
John,” is used in the manufacture of tazze, as shown in this 
case, and of vases as exhibited in the Hall. The visitor will not 
overlook the magnificent Vase No. 27 (p. 53) ; or the fine- 
collection of specimens of fluor-spar in the Ludlam cases (p. 13) . 
Case N. — Quartz. 
Occurring under a greater variety of aspects than any other 
member of the mineral kingdom, the species Quartz necessarily 
claims a large amount of space, and hence it extends through 
this and the three succeeding Cases. Pure quartz consists simply 
of silica, or silicon dioxide. The mineral crystallizes in forms 
belonging to the rhombohedral system, and is sufficiently hard 
to scratch glass with facility. 
Rock crystal is a pure transparent variety, frequently 
enclosing rutile, chlorite, various fluids, &c. Small brilliant 
crystals are often locally termed “ diamonds;” such for example, - 
are the so-called Cornish diamonds, Bristol diamonds, &c. 
Crystals which contain slender prisms of rutile, or oxide of 
titanium, known to the jeweller as filches d’ amour, or Loves- 
arrows, are polished as ornamental stones. A more useful 
application of rock crystal is the formation of “ pebble ” lenses - 
for spectacles. 
Smoky quartz is a variety presenting a brownish tint, the 
term morion being applied when the colour becomes intense. 
The transparent brown and yellow crystals form the well- 
known Scotch stone, called from its locality cairngorm ; whilst 
the bright yellow varieties are distinguished as citrine or false 
topaz. 
