CELESTINE

A sulphate which may contain traces of calcium and barium. It is usually sky blue in colour but may also be white/brownish yellow. It is the main source of strontium which is used in fireworks and flares because it burns with a red flame. It is also used in the manufacture of varnishes and household ceramics.

It is easily scratched (3-3.5 on the mohs scale) and derives it's name from it's celestial blue colour.

It is found in granites and pegmatites and may also be formed by the evaporation of salt water in closed basins. Here it exists with chalk and aragonite.

It is fairly common and was first discovered in Sicily in 1781. (Here it occurs in chalk and is usually white). The finest samples are now found in US. It may also be found in Russia, Tunisia, and UK (Gloucestershire).

CERUSSITE

A carbonate which is very beautiful but too soft to be used as a gemstone (3-3.5 on the mohs scale). It is very brittle and fragile. It is usually colourless or white but may also be blue/green/grey. It is a minor source of lead but is rarer than galena which is the main source.

It is a secondary mineral which forms by the alteration of galena in oxidised zones of lead veins. It may be found in association with galena, smithsonite and sphalerite. It usually forms in needle like shapes (acicular). Arrow head shaped crystals are very common. These form due to twinning which is when two crystals grow into each other.

It's name is derived from the Greek word keros which means wax.

The largest crystals were found in Namibia (over 10cm long). It can also be found in Sardinia, Australia, Siberia, Tunisia, US and Scotland (Strathclyde region).