Page 18 - Curriculum Visions Dynamic Book

Iron sulphide
Iron sulphide, or pyrite, is a common compound of iron, also known as “fool’s gold”. Pyrite is a very common mineral, occurring in many types of rock. It is commonly found in veins and can form perfect
cubic (cube-shaped) crystals.
Shale rocks contain pyrite because the
muds from which they are formed were once also combined with decaying organic matter. As the organic matter decayed, it took oxygen from the water, and hydrogen sulphide
gas was produced. The hydrogen sulphide reacted with iron in the
water to produce iron sulphide. In
the right conditions the iron sulphide grew into perfect cubic crystals; in other circumstances it developed into nodules.
Iron sulphide is not stable in damp air, where it readily oxidises to a brown colour. The shiny crystal that you see in the picture on the right will turn progressively grey and begin to crumble to iron sulphate.
Iron sulphide is not used as an iron ore, because its high sulphur content is difficult to remove. It is mainly used in the production of sulphuric acid.
 This is a typical sample of an ore. The conditions that allow the formation of pyrite are also right for the formation of crystals of other compounds. This is the reason refining ores is often a very complicated chemical process.
These transparent crystals are quartz.
A cubic crystal of pyrite. The parallel “scratches”, known as striations, are a common feature of pyrite crystals.
The dark crystals are sphalerite (zinc sulphide).
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