66 NEW YORK STATE MUSEUM 
magnetite itself, and contemporaneous with it, such as apatite, tour- 
maline, calcite, quartz, pyrite, pyrrhotite, and occasionally chalcopy- 
rite, are likewise mixed with the ore. Of these apatite is the com- 
monest and most abundant. In the few deposits where apatite is 
sparingly distributed it is usual to find the sulphides increased in 
quantity, so that the amount of sulphur in these magnetites appears 
to vary inversely as the phosphorus increases. 
The more or less altered minerals, remnants of still unreplaced 
rock, which are invariably mixed with all the magnetites except those 
which have replaced crystalline limestones by magmatic processes,” 
are quartz and feldspar, both frequently sericitized; hornblende, 
pyroxene and mica, all generally more or less altered by sericitiza- 
tion, chloritization and epidotization; magnesian-bearing pyroxenes, 
which are especially subject to alteration, with fine, flaky tale and 
serpentine as the products, and occasionally leucoxenized titanite. 
Seer plates, ©) 72010" tii.) 
Although the ore is, as stated, in general massive, compact and 
hard, it sometimes occurs as less coherent, granular aggregates more 
or less friable, known as “ shot ore,” and in rarer instances it is found 
crystallized in octahedra and in cubes. 
Sometimes the ore is massive, blocky, coarse and jointed, with 
planes of easy parting, so that it breaks out in straight-sided pieces; 
in zones affected by faulting the magnetite is crushed and more or 
less friable. 
When small pieces of the hard, compact, massive ores are ground 
to a plane surface and polished, it will be seen that they are com- 
posed of grains varying in diameter from i or 2 millimeters, in the 
dense, finely crystalline ores, up to more than I centimeter, in the 
coarser magnetites. Each grain is itself composed of an aggregate 
of minute crystals which have the same orientation in the individual 
grains, but each crystal aggregate will differ in orientation from the 
ageregates of adjacent grains, so that by holding the polished slab 
of ore in certain positions, light reflected from its surface will reveal 
the grain-size and varying orientations of the minute crystals com- 
posing the grains, whereas in other positions the surface looks 
structureless and uniform. This is especially true of the finely 
crystalline ores; the coarser ones have rather a prominent grain- 
difference, especially where sulphides are distributed interstitially 
111 The Tilly Foster, The Mahopac, the Croft, the Todd, the O’Neill, The 
Forshee, the Red-back (in part), are representatives of this type. 
