MAGNETITE MINERAL FACTS Nevada Turquoise gem stones
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Magnetite Mineral Facts:

Chemical Formula: Fe3O4
Magnetic Oxide of iron, Iron, 72.4 per cent

Colors: Black and streak is black as well.

Hardness: 6

Density: 5.2

Cleavage: No cleavage, magnetite breaks with an uneven choncoidal fracture. 

Crystallography: Cubic
Octahedrons common; also octahedra and
dodecahedrons, or combinations of the two. Also occurs in granular and massive forms.

Luster:. weak metallic or sub-metallic luster.

Optics: (Refractive Index):  Opaque

magnetite iron ore
Water worn and rough natural

Composition, Structure and Associated Minerals:
The mineral occurs as a constituent of many
igneous rocks and crystalline schists, and in lenses embedded in rocks of many kinds. It also constitutes veins cutting these rocks and as irregular masses produced by the dehydration and deoxidation of hematite and limonite under the influence of metamorphic processes.

It occurs also as little grains among the decomposition products of iron-bearing silicates, such as olivine and hornblende. The larger masses are either segregations from igneous magmas or deposits from hot solutions and gases emanating from them. The mineral weathers to limonite and hematite and occasionally to the carbonate, siderite.

As " black sands," magnetite occurs in placer deposits, as in the Yukon and Columbia rivers. Most placer gold deposits contain significant magnetic black sand. Most large deposits of magnetite occur as segregations in igneous rocks, chiefly in the more basic rocks, gabbros, norites and sometimes syenites, as at Taberg and Kiruna, in Sweden, at the Adirondacks in the United States, and in the Urals. Magnetite also occurs as lenticular bands, interfoliated with schists, as in Scandinavia, Urals, California, Saxony, etc.

Identification and Diagnostics
Magnetite is easily recognized by its color, magnetism, and hardness (6). The mineral is infusible before the blowpipe. Its powder dissolves slowly in HC1, and the solution reacts for ferrous and ferric iron. Strongly magnetic; sometimes exhibits polarity and is therefore a natural magnet, known as lodestone.

magnetite black sand

Magnetite, Magnetic black Sand

Occurrence, Localities and Origins:
A common and widespread ore of iron. It is found as an accessory mineral in rocks of all classes and sometimes becomes their chief constituent. Most commonly associated with crystalline metamorphic rocks, also frequently in rocks that are rich in ferromagnesium minerals, such as diabase, gabbro, peridotite. In many cases forms large ore bodies that are thought to be the result of magmatic differentiation; such bodies are often highly titaniferous. Occurs at times in immense beds and lenses, enclosed in old metamorphic rocks. Found in the black sands of the seashore. Occurs as thin plates and dendritic growths between plates of mica. Often intimately associated with corundum, forming the material known as emery.

The localities at which magnetite has been found are so numerous that only those of the greatest economic importance may be mentioned here. In the United States large lenses occur in the limestones and siliceous crystalline schists in the Adirondacks, in Warren, Essex and Clinton counties of northern New York; and in the schists and granitic rocks of the Highlands in New Jersey; and at Cornwall, Pennsylvania and at at Magnet Cove, Arkansas. Important foreign localities are in Norway and Sweden, where great segregated deposits are worked as the chief sources of iron ore in these countries. Magnetite occurs in Devonshire, Cornwall, and other localities in England, also in many places in Scotland and Ireland, and indeed in most parts of the world. Natural magnets or lodestones are found in Siberia and in the Harz Mountains of Germany. The magnetite is separated from the rock with which it occurs by crushing and exposing to the action of an electro-magnet.

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Please note that the author, Chris Ralph, retains all copyrights to this entire document and it may not be reproduced, quoted or copied without permission.

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