However, knowing that the vast majority of the people out there haven’t a clue what that means, I wrote him the following translation:
I am a Geologist who inflicts extreme heat and pressure on tiny amounts of powder (of known composition, which is similar to a specific rock type) for one to three weeks at a time. I then analyze the minerals which grew from the powder to determine which ones are present, and the precise composition of each. Once these experiments have been repeated for a variety of temperatures and pressures (each of which is comparable to specific depths under ground) it is possible to determine which chemical reactions are happening at which temperatures/pressures (for that specific composition). This information is then used (both by myself and by other geologists) to help calculate the temperatures and pressures at which real minerals in real rocks probably grew.