树枝状晶体主要是由铁的氧化物——磁铁矿组成。
The branch shape crystallite is mainly composed of iron oxides, i. e. magnetite.
然而，磁铁并不一定全是由金属或金属氧化物制成。
However, magnets do not necessarily have to be made of metals or metal oxides.
黑的铁氧化物(磁铁矿)：黑的铁氧化物发现有用的，特别在半金属的配方作为提高冷的摩擦力。在半金属的配方的通用的成分。
Black Iron Oxide (Magnetite) Black Iron Oxide is found useful, especially in semi-metallic formulas as an agent for elevating cold friction.
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