Unless your oven can reach temperatures of over 1200 F, you'll not be able to produce calcined clay. Do a bit of (google) research about this product...it's interesting!

(Looks at google again.) Yep, it's that hot. I must have seen a Celsius temperature and misread it as Fahrenheit. I was kind of surprised that water chemically bound in the actual crystal structure could be driven off at the ordinary oven temperatures I thought I had seen.

Apparently, cat litter is calcined already, just not to as high a temperature as Turface.