CHALK


Chalk is a sedimentary rock of biochemical origin. It is soft, white and porous. It formed in the deep ocean far from land via the gradual accumulation of the calcite shells of coccolithophores. Layers of chalk are known that are hundreds of feet thick, indicating extremely long periods of accumulation.

Note that many products called chalk are not calcite. Gypsum is a common replacement (for example the "chalks" used on blackboards), as is talc. True chalk, however, is always composed of minute crystals of calcite.

This site awarded
See Steve's video interview about asteroid capture at Moonandback:
Part 1
Part 2
Part 3

See Steve's blog

Ramblings
On The Future
Of Humanity


(recent post)
A Project Plan for Space Based Solar Power


You
can make a difference! Help President Obama, NASA, and the people of Earth. See the
Apophis Challenge for solutions to
- Global Warming
- Global Energy
- Man in Space
- Preventing the next Extinction Level Event

 


Copyright ©1995-2014 by Amethyst Galleries, Inc.
Site design & programming by galleries.com web services