Turquoise is a phosphate mineral (Phosphorous and oxygen) - mixed with Copper and Aluminium to give it the distinctive Blue-Green colour which gives it the name.
With a hardness of 5.0-7.0 on the Mohs Hardness scale, it is not a very hard mineral and is formed as s secondary mineral (grown from other minerals and the actions of acid). The Blue colour is attributed to the copper and the green attributed to iron in the mineral.
Turqoise is sensitive to solvents as it is a phosphate and therefore, perfume and cosmetics may affect the colour, skin oils and cleaning fluids can also harm this mineral, and it should not be worn on very sunny days. Turqoise can be scratched by other gems and should not be stored in an Airtight container.
Some examples of Turquoise are shown below.