Firestone is an indigenous rock to
Pern, found upon most of the planet. It is made up of three items: a crystalline
substance that allows the stone to keep its shape, a gray coke that lines
the stomach, and is eventually regurgitated by the dragon, and red-yellow
phosphine that, when ingested into a gas form, ignites when it comes into
contact with air. This item can only be used by dragons and firelizards,
as most other lifeforms would get sick. Queens do not chew, however. At
first this was said to keep golds from going infertile, but it was later
found out that the
eggbearers where just genetically unable to chew the substance.
When firestone is chosen for a dragon, it is ideal that the rock is big enough for the dragon to chew properly, while not being too big that it can't fit within its mouth. Also, the saying 'the worse it smells, the better is', is actually true. The best stone to look for is about the size of one's combined fists, with a healthy red-yellow color that doesn't crumble to the touch, but flakes slightly.
When a dragon chews firestone (or
sandstone, in the case of weyrlings), the stone is ground back on the dragon's
molars, before being swallowed and sent to the second stomach. In there,
powerful stomach acids liquefy the coke and crystalline parts of the rock,
while the phosphine is released into gas form. When the dragon exhales,
the gas escapes, catching on fire as it comes in contact with the air.
Once done exhaling all of the phosphine gas, the dragon will regurgitate
the coke and crystalline substance, as their second stomach leads to nowhere.
The dragon can hold it in for a bit, but they will become sick if they
are not allowed to regurgitate the ash.