Other
Webmineral.com: Mineralogy Database: Calcite Mineral Data
This site by David Barthelmy gives exceptionally detailed information on the mineral calcite, with photos and clear terminology, crystallography data, Dana and Strunz classifications and much more.
Wikimedia
Wikipedia: Phlogiston Theory
Wikipedia offers detailed information on the Phlogiston Theory, a discredited 17th century theory hypothesis regarding combustion.