NEW YORK MINERAL LOCALITIES D 
Gabbros, diorites and other basic igneous rocks. Rocks of this 
series have for their chief feldspar constituents the plagioclases ; 
both orthorhombic and monoclinic pyroxenes occur as com- 
ponent minerals. The formation of individual crystals takes 
place as the rock grades from finer to coarser structure and gives 
rise to strings or zones of crystallized minerals rather than 
pockets and cavities as is the case with granite. 
COMMON MINERALS FOUND IN BASIC IGNEOUS ROCKS 
magnetite labradorite garnet 
ilmenite enstatite biotite 
spinel hypersthene chrysolite 
albite pyroxene titanite 
anorthite 
Metamorphic rocks 
Gneisses. Typical gneiss differs but little in mineralogic com- 
position from typical granite, The mineral constituents are, 
however, to be found in larger and better formed individuals 
along zones of contact with crystalline limestone and local areas 
of magmatic segregation. 
COMMON MINERALS FOUND IN GNEISS 
graphite hematite ~  sillimanite 
chalcopyrite _ orthoclase cyanite 
pyrite albite allanite 
marcasite amphibole tourmalin 
quartz pyroxene staurolite 
corundum garnet muscovite 
spinel vesuvianite biotite 
magnetite zircon monazite 
rutile | andalusite apatite 
Crystalline limestones. The crystalline limestones are prolific in 
accessory minerals which occur disseminated through the mass 
of the rock, in pockets or vugs or in zones of contact between the 
limestone and an adjacent igneous intrusive rock. 
