Plasma
Specific Properties
Occurrence
Locations and Specimen
Further Information
Specific Properties
Occurrence
Locations and Specimen
Further Information
Document status: usable, incomplete
Plasma is a more or less evenly leek-green, slightly translucent to opaque chalcedony. Sometimes plasma is considered the green variant of jasper, and hence is supposed to be opaque. There is no strict taxonomy, however, so any green chalcedony that is not chrysoprase may be called plasma. Green translucent chalcedony used to be called prase, and some people still call it so, but today the meaning of the word has changed and refers to green macrocrystalline quartz.
Specific Properties
The color can be a bright to dark leek-green, and is caused by different embedded materials, typically chlorite or actinolite. I am not sure if chalcedony that is green due to other embedded minerals can be called plasma (except nickel-compounds, as that would be a chrysoprase).
Occurrence
Plasma forms nodules and amygdules in volcanic rocks. It can also be found as vein fillings.
Locations and Specimen
Plasma of good quality comes from the Deccan Traps in India.
Zimbabwe
This specimen from the Great Dyke in Zimbabwe is colored by chromium compounds which are certainly not the typical cause for the color of plasma. Chromium bearing chalcedony is sometimes called mtorolite. Its coloration is irregular and cloudy and there are more dark and translucent as well as brighter and more grainy parts, giving the specimen a somewhat layered appearence. The walls of the cavities are covered by small quartz crystals.
Further Information, Literature, Links
