What type of stone do targets of Flesh to Stone, and Petrification, turn into?

Question

To what kind of stone creature or character is turned with petrification or flesh to stone type spells?

The Petrified condition is the result of various monster abilities

A Petrified character has been turned to stone and is considered unconscious. If a petrified character cracks or breaks, but the broken pieces are joined with the body as he returns to flesh, he is unharmed. If the character's petrified body is incomplete when it returns to flesh, the body is likewise incomplete and there is some amount of permanent hit point loss and/or debilitation

The flesh to stone spell reads:

The subject, along with all its carried gear, turns into a mindless, inert statue. If the statue resulting from this spell is broken or damaged, the subject (if ever returned to its original state) has similar damage or deformities. The creature is not dead, but it does not seem to be alive either when viewed with spells such as deathwatch.
Only creatures made of flesh are affected by this spell

Is it one of the sedimentary stone types (came from organic elements) or some other like igneous or metamorphic?

And to which subtype of stone are they turned?

More on stone types on https://en.wikipedia.org/wiki/List_of_rock_types

Answer 1

It's not stated explicitly, but limestone or marble seems the best fit

I'm not aware of any material that explicitly answers this, but the material components for the flesh to stone spell are "lime, water, and earth."

"Lime" is calcium oxide or calcium hydroxide, typically manufactured from limestone and mixed with water and sand/gravel to make concrete. Already limestone seems like an obvious fit.

Statues are commonly made out of marble… and that happens to be a metamorphosed form of limestone. This is also a strong contender.

Limestones and marbles are based primarily on calcium. As well as being present in the material components, it's also found in the human body in large quantities (in bones, in teeth, and as an important electrolyte). Humans are about 1.5% calcium by mass.

On the other hand, most other rocks involve significant quantities of silicon, but that's only a trace element in the human body (<0.1% by mass), and silicon isn't listed in the material components. ("Earth" could be just about anything from gravel to mulch; some would contain silicon, others wouldn't.)

So, going by both the material components and the human body, we're probably looking at a calcium-based rock without large amounts of silicon, which implies limestone or marble. It could even be concrete—it's a rock, though not a very romantic one.

I'm told (h/t Molot) that "In one of the Underworld books (prose, not rules) drows turned victims into onyx". While true onyx is a silicate, most "agate" sold today is in fact calcite (calcium carbonate), commonly found within limestone, so this is still consistent with the "calcium-based rock" interpretation.

If you want to enforce conservation of mass, then this fine answer's suggestion of pumice is definitely the best option, but spells are generally not known for respecting conservation of mass. For example, Iron Body multiplies a person's weight by ten.

Answer 2

This is a great question! Do they turn into the stone of the bedrock nearby? Do different organs become different kinds of rock? In my game, I probably wouldn't specify unless someone at the table asked - in that case, I would probably allow the magic-user to specify.

However, as a geologist, I am very tempted to answer this question in a more definitive way. Assuming we have conservation of mass, what kinds of stone could a person become. Humans are roughly water, so I'll look for rocks and stones with a similar density. In geology, we have a very simple statistic called Specific Gravity that relates a mineral or rock to the density of water. A specific gravity of 1 = water, while a 3 would be 3x as dense. Most rocks are around 3 or 4.

Coal is right around 1.1, but I don't think thats right, because I think petrified creatures are resistant to fire damage (that said, if you're looking for a stone with the exact elemental composition as a human body, look no further). Baked or calcined clay is right around 1.6 but is just a bit too dense, maybe with hollow bits. I think the rock we are looking for is porous or vesiculated pumice: because of its porosity, its specific gravity varies by a lot, but can be as low as .8, which means it floats!

So, for complete 100% fantasy realism, your petrify spell probably animals into pumice, which is an extrusive igneous rock.