Don't think I will be much help but I will try to explain
what I think I know. lol
I was trained in electronics where you have to imagine
atomic structure in your mind. It's the electrons that supposedly
create the current when driven by a potential (voltage).
I am not trying to equate heating silica to electronics but trying to
instill the thought of imagining the atomic structures of silica's/feldspars (clay)
and the other materials that get mixed with them. Cherts are not as pure as clear
refined glass. Obsidian is not as pure as glass.
I have come to imagine the crystals not really altering to much with low heat like 500 F because they are created under high pressure and extreme heat. (I think)
Obsidian is quick cooled molten lava. Cherts/flints/agates/jaspers are usually created in ancient marine environments via permineralization. Minerals perculating through the earth and getting deposited in limestone cavities.
Long story short-- I imagine the impurities amongst the crystals being reheated to a point where they sort of smooth out and re-glue the crystals together. This is the simple explanation as to why the flakes become more slick and lustrous.
As for abo vs kill I think you will have to use your imagination just because one is controlled and the other not so much. I recommend the kill because there are charts for time and temp. I use my oven.This keeps the losses minimal.
Here is a taste of the Wicki explanation---
Zuma
Silicon dioxide - Wikipedia, the free encyclopedia
https://en.wikipedia.org/wiki/Silicon_dioxideSome explanation in nature---
The only stable form under normal conditions is α-quartz and this is the form in which crystalline silicon dioxide is usually encountered. In nature impurities in crystalline α-quartz can give rise to colors (see list). The high temperature minerals, cristobalite and tridymite, have both a lower density and index of refraction than quartz. Since the composition is identical, the reason for the discrepancies must be in the increased spacing in the high temperature minerals. As is common with many substances, the higher the temperature the farther apart the atoms due to the increased vibration energy.
The transformation from α-quartz to beta-quartz takes place abruptly at 573 C. Since the transformation is accompanied by a significant change in volume it can easily induce fracturing of ceramics or rocks passing through this temperature limit.
The high-pressure minerals, seifertite, stishovite, and coesite, on the other hand, have a higher density and index of refraction when compared to quartz. This is probably due to the intense compression of the atoms that must occur during their formation, resulting in a more condensed structure.
For the Chemist lol Not for me
For example, in the unit cell of α-quartz, the central tetrahedron shares all 4 of its corner O atoms, the 2 face-centered tetrahedra share 2 of their corner O atoms, and the 4 edge-centered tetrahedra share just one of their O atoms with other SiO4tetrahedra. This leaves a net average of 12 out of 24 total vertices for that portion of the 7 SiO4tetrahedra that are considered to be a part of the unit cell for silica (see 3-D Unit Cell).
