PYROMORPHITE

A phosphate of lead which may also contain some chorine and oxygen. It is a member of the phosphate group and is usually very heavy and green in colour due to its lead content. (Some specimens may also be brown, grey, orange or yellow) Some impurities in tap water can cause a deterioration of its colour. Its name is derived from the Greek words pyr, which means fire, and morphe, which means shape. These refer to the fact that when heated and left to cool the mineral will alter its form. It is fairly soft (3.5-4 on the mohs scale) and was previously known as green lead.

Although it has no industrial uses it has an attractive appearance. Sometimes crystals appear in the shape of green barrels. The scientific name for this is campylite and such specimens are the most sought after by collectors. Pyromorphite often occurs in association with mimetite and it is sometimes difficult to tell the two minerals apart without chemical analysis. This can be done by heating since mimetite gives off a strong garlic like smell when heated because it contains arsenic whereas pyromorphite gives off no odour.

It forms when preexisting minerals (mainly galena and anglesite) are altered in the oxidized zones of lead veins. Therefore it is classified as a secondary mineral. If it acquires an atom of arsenic it will become mimetite. It can be found at Broken Hill, New South Wales, Australia and in Germany and in the Leadhills, Scotland.

PYRRHOTINE

An iron sulphide mineral which is usually made up of one atom of iron and one of sulphur. It is normally bronze yellow in colour but darkens to reddish bronze when exposed to light. It is relatively soft (3.5-4 on the mohs scale) with a metallic lustre and is also known as magnetic pyrites. Although worthless in its pure form if it contains impurities of cobalt, nickel and platinum it may become hugely valuable. If these are found in significant quantities then it can be mined on a commercial scale.

Cobalt is used in alloys to strengthen other minerals and is a component of stainless steel. Nickel is also used to strengthen steel. Mumetal is an example of a magnetic alloy used in electrical transformers. It is made up of 78% nickel, 17% iron and 5 % copper. Platinum is rare, beautiful, heat resistant and unreactive to other chemicals. It is used as a component of electrodes and sparking plugs and by dentists as a filling.

Apart from magnetite, pyrrhotine is the only common magnetic mineral. When extracted it may have iron surface stains which can be removed with oxalic acid. Surface calcite growths can be removed with hydrochloric acid.

It occurs in igneous rock, particularly in gabbro where it is associated with chalcopyrite, galena, pyrite and sphalerite. It may also be found in metamorphic rocks, pegmatites and in some meteorites. It can be found in countries such as Austria, Bolivia, Brazil, Canada, Germany, Italy and Sweden.