ngth: 205 psi; ASTM C482 modified. 5. Modulus of Rupture: 2,110 average, ASTM C99. 6. Mohs Hardness: 6.5-7.5; scratch test. 7. Absorption: 0.022%; ASTM C97. 8. Stain and Acid Resistance: Not affected; ASTM D2299. 9. Surface Burning Characteristics: Flame spread = 10, smoke density = 195; ASTM E84. 10