NEW YORK MINERAL LOCALITIES 6 
Secondary minerals 
Secondary minerals, developed as a result of chemical action 
on previously formed rocks, are, to a large extent, deposited by 
percolating water. With regard to their mode of occurrence 
they may be classified as follows: (1) concretions; (2) deposits 
lining the interior of cavities, vugs, caverns and grottos; (3) 
vein formations; (4) minerals produced through pseudomor- 
phism and paramorphism. 
Concretions. Concretionary deposits of mineral matter are 
frequent in rocks of sedimentary origin. They are in general 
formed by the deposition, in successive layers around some or- 
ganic center, of mineral matter leached from the surrounding 
rock. The calcium carbonate concretions found in clay beds are 
excellent types of this form of mineral occurrence. Concre- 
tionary forms of quartz, siderite, pyrite, chalcocite etc., are also 
formed in sedimentary rocks. 
Deposits lining the interior of cavities, etc. The formation of 
secondary minerals in cavities of various origin results from the 
chemical action of percolating water on the rock adjacent to 
and forming the walls of the cavity. The soluble mineral matter 
is dissolved from the rock traversed by the descending surface 
water to be redeposited, sometimes in an entirely different form 
in the open spaces. The minerals thus deposited take the form 
of distinct crystallizations or of concentric, incrusting masses. 
COMMON SECONDARY MINERALS OCCURRING IN CAVITIES 
hematite barite apophyllite 
limonite celestite stilbite 
quartz anhydrite chabazite 
calcite gypsum heulandite 
dolomite serpentine harmotome 
siderite '. sulfur analcite 
aragonite datolite natrolite 
strontianite prehnite 
Vein formations.'_ Mineral veins may, with justice, be con- 
sidered as constituting'a division under the last named class of 
Secondary mineral deposits; the distinctive character of the 
1The formation of mineral veins has been very fully discussed by Posepny, F. 
Genesis of Ore Deposits. Am. Inst. Min. Eng. Trans. 1893. p. 23-197. 
