Where Does Chrysotile Form?   

Chrysotile, the most commonly used asbestos mineral, has been mined extensively in Russia, Canada, China, Zimbabwe and South Africa.

Where Does Chrysotile Occur?

Chrysotile is one member of a family of sheet silicates called serpentine.  Rocks that are composed principally of serpentine are called serpentinites.

Serpentinites are METAMORPHIC ROCKS    that are formed when hot water reacts with  an igneous rock called PERIDOTITE   .

Although the whole rock contains serpentine, long fibers of chrysotile serpentine are only found in VEINS   .

The fibers of chrysotile are oriented in specific directions within the vein, with most of the fibers running perpendicular to the vein wall.

Why Does Chrysotile Only Form from the Metamorphism of Peridotite ?

The chemical building blocks of serpentine are:

3MgO . 2SiO2   2H2O.  

The ingredients for serpentine are 3 magnesium atoms for every 2 silicon atoms.

For Serpentine...     Mg : Si = 3 : 2

However, in the Earth's CRUST silicon is far more abundant than magnesium.

For the Crust...      Mg : Si = 1 : 19

Rocks are composed of minerals, and the minerals are composed of the atoms that were present when the rock formed. Thus serpentines can only grow in rocks that have abundant magnesium, along with silica and a source of water.

Although magnesium is scarce in the crust, it is an element that is abundant in the MANTLE  , which is composed of the water-free rock called peridotite. Magnesium-rich silicate rocks are rare in the Earth's crust. 

Chrysotile and other serpentine minerals only grow in abundance in peridotites because they are the only silicate rocks with enough magnesium.

The only problem is how do you get these dry peridotites up and out of the mantle and add the water...

© 2001 Wayne G. Powell