An extraordinarily beautiful purple - blue gemstone (typically found in only one country in africa), with a hardness close to or less than 7.0 that is often formed by heat treatment of a brownish or greyish silicate mineral is a gem variety of

1) zoisite
2) cordierite
3) thulite
4) tourmaline
5) feldspar

4) tourmaline

Explanation:

It is a gemstone that is found on the African continents and is made pos the silica materials and has compounds of the aluminum and iron and the potassium lithium and the sodium and this is classified as a semi-precious stone. The metamorphic rocks and the sandstone consists of these minerals and the colors of the gemstone cane alter by the heat treatment.