ABSTRACT
Tourmaline is a crystalline boron silicate mineral that incorporates elements such as aluminium, iron, lithium, magnesium, potassium or sodium. It is a semi-precious stone which exhibits a wide variety of colours including dichroism, in that they change colour when viewed from different directions. Red beryl is found in topaz-bearing rhyolites while beryl gems are ordinarily found in pegmatics and certain metamorphic stones. Synthetic laboratory-grown stones with the same chemical and physical properties as natural alex-andrite can be produced. Opal is a hydrated amorphous mineraloid of silica deposited at a relatively low temperature found in the fissures of almost any kind of rock in association with basalt, limonite, marl, rhyolite and sandstone. Aquamarines are explored in areas that contain Precambrian metamorphic rock which may contain many minerals such as biotite, felspar, garnet, mica, quartz and many gem-stones within it. The metamorphic rocks comprise some pegmatitic veins that host aquamarine crystals.
