Is opal an intrusive or extrusive mineral?

Answer 1

Opal is not considered a rock but actually a mineraloid gel. It is deposited at relatively low temperatures. One of the characteristics if igneous rocks, sometimes called fire rocks, is that they are formed at high temperatures. Whether an igneous rock forms below ground, or on or near the surface, it's all about heat forming the rock. Opal cannot take its form under that kind of heat.

Answer 2

Emerald is considered a mineral. Minerals are not considered rocks, though they can be found in them. Emeralds are formed in veins of magma that has flowed into the crust and formed a vein. As is cools it forms crystalline structures. Emeralds form here as well as many other minerals.

Answer 3

An opal is not a metamorphic rock - it's a mineraloid gel which is deposited at relatively low temperature and may occur in the fissures of almost any kind of rock, being most commonly found with limonite, sandstone, rhyolite, and basalt.

Answer 4

Opal is actually a mineraloid gel, not a mineral or a rock by their definition.

Answer 5

Opal is not a rock, but a mineraloid gel.