Agate High-quality orb from the north of Madagascar exhibiting contrasting bands representing the growth that has taken place over millions of years. Agate is banded chalcedony, a form of microcrystalline quartz made up of twisted crystal fibres. Forming within the cavities and veins of lava, Agate replaces other mineral deposits and limestones and mostly found within volcanic lavas.
Jasper is a Quartz, a microcrystalline mineral which may be botryoidal, mammilary, and stalactitic formations, and may be found as smooth rounded pebbles or nodules.
The most explosive volcanoes produce ashes or tuffs, creating a mixture of ash, lava and sediments which are torn from the surrounding rocks. It's thought that micro-shards of silica in glass form produced by erupting volcanos which produce ash and tuffs, eventually release silica that permeates through old underlying lava cavities through atmospheric and rainwater and can also include decomposing of vegetation and animal matter within the sediments deposited between eruptions.