What rock forms most caves and caverns?

The cave itself of course, as a geological entity.

In limestone:

The rock's internal structures such as its bedding-planes, joints, folds, faults and any fossils (since most caves are in limestone).

Precipitated calcium-carbonate 'speleothems' (stalactites, stalagmites and related formations)

Sediment banks - laboratory analysis which can give a lot of information on the cave's own development, palaeoclimate, etc (ditto with speleothems).

In lava caves:

The rock itself, and stalactite-like formations from lava dripping before it solidified.

By the way, why has Answers logged this as being in "Geology, Labour and Birth, Speleology"? I never realised human reproductive Biology is a topic within karst geology!