MISCELLANEOUS NONMETALLIFEKOUS MINEEAL LANDS. 139 



The geologic occurrence of the minerals named in the foregoing 

 list is very diverse and the characteristics of the deposits containing 

 them will therefore be referred to but briefly. Many of them exist 

 in stratified or bedded form. Limestone, building stones, some 

 cement materials, and some ornamental stones occur as sedimentary 

 or metamorphic rocks. Slates are obtained usually from beds and are 

 quarried in much the same manner as other building stone. Some 

 glass sand is made by crushing a loosely consolidated sandstone or is 

 obtained from beds of loose sand. Gravel is usually found in more or 

 less bedded form in so-called " gravel banks." Volcanic ash and 

 diatomaceous earth are ordinarily found in stratified deposits or 

 beds. Clays, including kaolin and fuller's earth, result from the 

 accumulation of the less soluble residues of the decomposition of pre- 

 existing rocks and minerals and are obtained almost entirely from 

 bedded deposits. Some clays are obtained by dredging the bottoms 

 of streams or lakes. Kaolin in its purest form results from the resid- 

 ual decomposition of pegmatitic feldspar in place. 



Gypsum, borax, and halite, or common salt, are found in deposits 

 that are related with respect to the manner of their geologic occur- 

 rence. They are found most abundantly in association with stratified 

 rocks and are regarded as chemical deposits resulting from the evapo- 

 ration of waters of inland seas and lakes. Some deposits of borax 

 and halite occur in more or less stratified form in the beds of present- 

 day salt lakes or marshes. Sulphur deposits large enough -to be of 

 economic importance occur as products of volcanic activity and are 

 found near volcanic craters and also near some hot springs, either 

 active or extinct. 



Monazite, owing to its minute crystalline form and great weight, 

 occurs in greatest quantity where it has been concentrated in placer 

 deposits. 



Talc and soapstone are very soft minerals which have presumably 

 resulted from the alteration of other minerals. ' Soapstone, a talc 

 schist, occurs with other rocks of various kinds, usually crystalline or 

 metamorphic; talc occurs in beds intercalated in schistose limestone 

 and in lenses or pockets in certain intrusive rocks. 



Many minerals exist in veins or in the form of lode deposits. 

 Quartz, feldspar, cryolite, mica, and some gems are found in veins 

 in crystalline rocks. The strontium minerals occur principally in 

 lenses, in granular and columnar masses, in bedded deposits, and 

 in crystals that form nests and geodes in limestone. Fluorspar is 

 found, as a rule, in veins in limestone, gneiss, schist, and sandstone. 

 It is a common gangue of metallic ores, particularly those of lead, 

 zinc, and tin. Barytes occurs in veins and beds associated with other 

 ores, as well as in veins and masses in limestone. 



