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Posted by: Donald Kasper
A variety is a gem term of a colorized mineral of the same overall chemical composition.
Agates are full of calcite, clay, opal, moganite and silica polymorphs.
In infrared, agates have opal-CT and opal-C and I model three new species of opal. No agate on this planet has opal-A. Why not? Opal-A is the only opal formed with hydrothermal solutions and from weathering. I have a very specific key to identify opals in infrared and can see mixed forms which occur all the time.
In infrared, agates have two populations of moganite. I model one is alpha-moganite, the other is beta-moganite. Raman reports they are both moganite and cannot tell alpha from beta. The alpha is only in the banding, and the other is immiscible in the agate, and found in specific structures such as microspheres.
In infrared, I have proposed that beta-silica minerals can be found, and have shared that data with Caltech, Pasadena Planetary Science group. If correct, agates have beta-quartz. No beta-cristobalite, but that is found in geode shells. But waterlines can have opal-BC (opal-beta-cristobalite). In fact, the only place geologically you can ever find an opal-C in volcanic systems, is in the waterline structures of geodes/amygdules. No where else. The opal is a supercritical transition opal form and lives right there.
Agates have celadonite and bentonite. Foggy white agates can be beta-moganite rich or can be calcite-agates.
So these are multi-mineralic and as such are rocks. They are very complex rocks of mixed composition of many quartz and clay polymorphs. The minerals occur in specific structures that you can find if you use spot reflectance infrared to aim specifically at them.
Claims agates are 99% quartz is a farce, and Moxon needs to stop promoting that. He is saying that if you bash you agate to bits and pick out the quartz, it is very pure quartz. But, this is not what an agate structure specimen is, and falsely dumbs down the conversation to promote this varietal garbage. Agates have as little as about 40% quartz, which makes them rocks. This means I am talking about the actual, whole specimen, not the banding only. The inclusions tell the rest of their story of formation as each included mineral has specific, known conditions of formation.