Provide your best answer for the following question. Give ONLY the answer, no other words or explanation.
For example:

Answer: <most likely answer, as short as possible; not a complete sentence, just the answer!>.

The question is: Intense heat and pressure in Earth's crust can change sandstone into quartzite. During this metamorphosis, many properties of these rocks change. Which property of these rocks will most likely remain the same?
mass
Crystalline structure.