Page 7 - Curriculum Visions Dynamic Book

Where lead is found
Lead is widespread, occurring in the same location as other metals such as gold, silver and zinc. It mainly occurs as the mineral galena (lead sulphide, PbS), and also as cerussite (lead carbonate, PbCO3) and anglesite (lead sulphate, PbSO4).
Most concentrated metal deposits are formed in hydrothermal veins, that is, fissures in rocks sited above magma chambers. As hot mineral-rich fluids rise from the magma chambers during the last stages of volcanic activity, the fluids cool and a number of minerals solidify, among them lead. For this reason, ore mines usually recover a variety of metals.
Lead mines are sometimes found in areas of limestones (especially a form called dolomite) that once had magma chambers below them. Limestones have many natural fissures through which hot minerals can easily flow.
density: the mass per unit volume (e.g. g/cc).
hydrothermal: a process in which hot water
is involved. It is usually used in the context of rock formation because hot water and other fluids sent outwards from liquid magmas are important carriers of metals and the minerals that form gemstones.
magma: the molten rock that forms a balloon- shaped chamber in the rock below a volcano. It is fed by rock moving upwards from below the crust.
mineral: a solid substance made of just one element or chemical compound. Calcite is
a mineral because it consists only of calcium carbonate, halite is a mineral because it contains only sodium chloride, quartz is a mineral because it consists of only silicon dioxide.
sulphide: a sulphur compound that contains no oxygen.
vein: a mineral deposit different from, and usually cutting across, the surrounding rocks. Most mineral and metal-bearing veins are deposits filling fractures. The veins were filled by hot, mineral-rich waters rising upwards from liquid volcanic magma. They are important sources of many metals,
such as silver and gold, and also minerals such as gemstones. Veins are usually narrow, and were best suited to hand-mining. They are less exploited in the modern machine age.
 The cubic structure and dull grey colour of lead sulphide shows very clearly in this specimen.
Galena
Lead sulphide, or galena, is easily spotted by its dark grey cubic (box-shaped) crystals.
Galena is soft. When it is rubbed against a surface, it leaves a grey streak of colour, showing its lead content. Like other lead compounds, galena is very heavy.
Galena is the main source of lead for the world’s industries.
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 Lead metal is bluish, but it readily oxidises in the presence of air to a dull grey. In polluted air it turns dark grey to black.