You may have heard that tmp3 (formerly pavg0) controls TUNG, GLAS, and QRTZ breaking; this thread explains how that works.  Pressure changes set the tmp3 value for the aforementioned elements and after manually setting the tmp3 values of the elements, I have found the minimum tmp3 values that cause breaking; I call these tmp3 values "breaking points" and here they are:

TUNG:  tmp3=33+

GLAS (brush-spawned):  tmp3=17+

GLAS (chemically strengthened at maximum strength ouside of reaching it with console):  tmp3=251+

QRTZ (brush-spawned temp):  tmp3=315+

QRTZ (absolute zero temp):  tmp3=1+

QRTZ (maximum temp before melting):  tmp3=2745+

GLAS's breaking point rises and lowers with it's life; I assume you've read the tpt wiki so I don't need to go into detail how it's life mechanic works.  QRTZ's breaking point rises and lowers with it's temperature; the tpt wiki mentions that it becomes brittle when cold but not that it becomes tough when hot; there is, however, one save that demonstrates that by dropping THDR on heated QRTZ.  Incredible to think that QRTZ is both the weakest and the strongest breakable element in tpt--that breaks under pressure changes anyway.