Magnetite is an ore iron oxide (Fe3O4) found in igneous, metamorphic and sedimentary rocks. In its detrital state -- ground into debris by the action of water -- it becomes a rough sand such as the black sands found on the beaches of Auckland, New Zealand. Magnetite is also considered a natural magnet and has many other unique characteristics.
Luster
Magnetite's luster, or sheen, may appear either metallic or non-metallic (rock like). The surface will appear either shiny or dull, waxy or iridescent.
Hardness
On the Mohs hardness scale, which rates hardness of minerals from 1 (soft) to 10 (hard), magnetite falls between 5.5 and 6.5. Magnetite is about as hard as feldspar, which is harder than apatite but softer than quartz.
Color
Color is one of the attributes geologists use to distinguish one mineral from another. Magnetite's color runs from a dark gray to black.
Streak
Streak describes the color of the powder created from pulverizing a mineral. It can also be found by rubbing the mineral on a white ceramic tile or plate. Magnetite's streak is black.
Cleavage
Cleavage illustrates the way minerals consistently split, either evenly in one direction or in multiple directions. Magnetite usually has no cleavage, although a few specimens have been known to have eight-way splits, meaning they break apart into eight uneven pieces.
Fracture
Fracture depicts the way mineral surfaces look when shattered. Magnetite appears conchoidal, or smooth, with shell-shaped convex and concave surfaces, like obsidian --- a black, volcanic glass with smooth, shiny surfaces formed by rapidly cooling lava.
Magnetism
Geologists and mineralogists check for magnetic properties. Since magnetite is attracted to magnets, it is considered a natural magnet.
Specific Gravity
Specific gravity tests a mineral's mass compared to water. Magnetite registers an average specific gravity of 5.1, in the same range as hematite and pyrite. Magnetite has a higher specific gravity than sulfur, quartz and calcite, and a lower specific gravity than cobaltite, cinnabar and gold.
Crystal System
Crystal systems describe a mineral's crystal formation. Magnetite has an isometric crystal system, meaning the crystals are symmetrical.
Transparency
Minerals fall into one of three levels of clarity. They are either transparent (diamonds and glass), translucent or milky, (opals and chalcedony) or opaque (jasper and turquoise). Magnetite is an opaque mineral.
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