Occurrence
At Franklin magnetite is found here and there, associated with or taking the place of franklinite in parts of the zinc-ore deposit, or forming lenses of granular iron ore, or in some places disseminated in limestone. Good crystals showing o and d were found associated with chalcocite and silver (see page 26) in ore of the Parker mine.

In the iron-ore bed underlying the zinc-ore deposit on its west side magnetite is the principal ore mineral, massive for the most part but in places crystallized on the walls of vugs. In such a vug from the Gooseberry mine the crystals of magnetite are attached to hornblende together with pyrite, the hole having been filled with calcite. The ore of this bed, as shown by analysis 1 above, contains merely traces of zinc and manganese.

Magnetite is a constituent of the pegmatite, at some places only in minute amount but at others in considerable abundance, giving the rock a dark color.

At Sterling Hill magnetite is found chiefly in the pegmatite. It also occurs disseminated in the limestone and in isolated bunches of ore between the two legs of the zinc-ore body. Analysis 2 shows such ore to contain considerable amounts of zinc but little manganese. Other phases intermediate between magnetite and franklinite—namely, magnofranklinite, poor in zinc and high in iron and manganese—are referred to under the description of franklinite.