How to find the change in volume of a solid to a liquid

[NullusSum]

TL;DR

I need help finding the density of a liquid substance based on its original density as a solid. I believe I could acquire this from the change in volume during the solid to liquid phase. In my example, I used a specific composition of granite, and broke it down into its compound and elemental mass contributions.

Greetings. This is my first post here. I hope I can get some assistance for my problem.

Context​

Just to preface, this is just for a hobby and not any kind of homework or professional problem. With that said, I have been writing calculation step-by-step guides on phase changes in an effort to teach myself the methods. In my chemical composition guide, I use granite that is composed of 60% orthoclase, 30% quartz, 5% hornblende, and 5% biotite. From this, the density and mass contribution fractions of these mineral compounds were used to calculate the density of solid granite (~2.617 g/cm³) which I had planned to apply universally in the different phase changes.

Problem​

Provided I can find the specific heat capacities of each element in their solid state, I believe proceeding from here with finding the energy to melt granite is easy enough. However, where I faltered is I did not consider that the density of granite would not be persistent in vaporization due to the change in volume a solid to a liquid undergoes. The value I acquired is strictly for granite in its solid form, not liquid/molten granite. So if I wished to continue on from here, I would have to obtain the liquid density of the mineral compounds.

Help​

Because information that is usually this specific is not available online, I would like to inquire if there is a seamless way to calculate the change in volume of a solid to a liquid. It would not have to be exact, but rather, just a general rule of thumb equation, like a ratio, would be sufficient for my guide. However, if such a method is non-existent, I would greatly appreciate some pointers in the right direction. Also, since my example is rather specific, I can elaborate on it if needed.

 

[Chestermiller]

Have you considered doing it experimentally?

 

[Bystander]

https://en.wikipedia.org/wiki/Granite

 

[NullusSum]

Have you considered doing it experimentally?

I had not. That would probably be too ambitious for the scope of my small project. Especially for a layman like myself who is now only scratching the surface of these concepts, or at least that is how I view myself. My goal was to rely on preexisting data to solve for the [phase change] energies of granite mathematically. Do you think experimentation on my end is the only path to finding the answer I need?