{ 39 J 
Salts in Spires and other Figures, and abound in 
many Parts of England . 
Selenites, (thefe Stones have been frequently call¬ 
ed Lapides Speculates ) the Moon-ftone is of a 
brighter Colour than the Spar, and is tabulated, 
or can be feparated into thin Plates; they are fre¬ 
quently found in many Parts of the World, in Eng¬ 
land x in the Clay-pits in Staffordjhire, and particu¬ 
larly many of them in a blueifh Clay near Harbo- 
rough in Oxfordfhire. It has been faid that the 
Chinefc Moon-ftone fuffers Increale and Diminution 
in Sympathy with the Increafe and Decreafe of the 
Moon. 
Gypfum is a Stone of this Kind, but lefs tranfpa.- 
rent, and more eafiiy calcined, yielding a fine white 
Powder, of which is made Plaifter of Paris, a 
Commodity well known : it abounds in Dorfetjhire? 
and fame other Parts of England . 
Cryftalla. 
Cryftals are clear tranfparent colcurlefs Stones, 
generally found on high Mountains, Rocks, and 
in Mines; by a chemical Diffolution they yield 
Chalk and Sait. The Perfection of Cryftal confifts 
in its Luftre, Tranfparency, and Hardnefs. It is 
applied to various Ufes, being often manufactured 
into Boxes, Cups, and other Toys. Thole that 
have Straws, Duft, &c. encloled in them, are molt 
curious and rare, but leaft fit for Ufe. Naturaiifts 
deem the purely Cryftal ro be the original Matter 
of ail the precious Stones of the higher Gaffes, 
which being in a certain Degree influenced by diffe¬ 
rent mineral and metalline Qualities, thence affume 
their Variety of Colour and Hardnefs, and are 
called by their feveral diftinCt Names, as will be 
C 4 fhewn 
