It is very sensitive to pressure and high temperatures, hot baths, acids and alkalies. It has a vitreous to greasy luster. In the best quality the color is regularly distributed, but it is usually spotted or striped. In Chilean and Russian stones, the protruding white calcite diminishes the value. Well distributed fine pyrite is advantageous and is taken to show genuineness. Too much pyrite causes a dull, greenish tint.
Mineable deposits are rare. For centuries the most important deposit with the best qualities has been in the West Hindu Kush mountains of Afghanistan near the source of the river Amu-Darja. Lapis lazuli is mined under primitive conditions and in difficult terrain where it is present as an irregular occurrence in limestone.The Russian deposits are at the south west of Baikal Lake. The matrix rock is white dolomitic marble. Chile supplies lower quality stones with many white spots of calcite. The deposits are north of Santiago.
Lapis was used for jewellery in antiquity. During the Middle Ages, it was also used as a pigment to produce aquamarine. Some castles have wallpanels and columns covered in lapis. Today it is used for ring stones and necklace, Chilean lapis is used for carvings and ornamental objects.

*Info by Walter Schumann “Gemstones of the World”