Where does calcite come from?
Do you mean where is it mined? or how is it formed. Here is some information on calcite.
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http://72.14.205.104/search?q=cache:ZrcGr_MqzKsJ:www.cosis.net/abstracts/EGU05/09713/EGU05-J-09713.pdf+calcite+formation&hl=en&ct=clnk&cd=2&gl=us&ie=UTF-8
http://www.dailytimes.com.pk/default.asp?page=story_6-6-2005_pg6_8