John Riddall was asking about lodestone, or magnetite.
Where this occurs in large deposits, it is currently mined as a
valuable source of iron, such as in the underground mine at
Kiruna, Sweden, where production has for years exceeded
20 million tons a year. It tends to be fine-grained, so has to be
"pelletised" before being fed to a blast furnace, but when
heated in a pellet plant is "environmentally friendly" in that
it oxidises further to hematite in a reaction which generates
heat, so the consumption of oil to provide the necessary heat
is kept to a minimum.
Another major source, again mined underground, is at Krivoy
Rog, in the Ukraine.
The name lodestone has its origins in Anglo-Saxon, "lode"
being a "way". The same word crops up in lodestar -- the
stone, or the star, show the way.
I like the fact that magnets, magnetism, etc, are named after
the mineral "magnetite", and not the other way round. It is not
called magnetite because it is magnetic, but magnets are
called magnets because they behave like magnetite.
The mineral name comes from the ancient Greek "magnetis
lithos". They mined it in a district of Lydia called Magnesia.
I do not know the geology of the area, but I guess there were
veins of magnetite running through deposits of dolomite, which
is also called magnesian limestone. So that part of Greece
gave its name to both a magnetic mineral (and hence all
magnetic phenomena ) and also to the metal magnesium.
Tony Brewis
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