Terracotta

Hardened clay currently has no known use other than as an aesthetic block, somewhat of a cross between clay and bricks. It can be obtained by smelting clay.

Behavior
Hardened clay has an above-average resistance towards explosions. Unlike normal clay, a wall of 4 hardened clay blocks thick can withstand a direct TNT or creeper explosion while only one column would be destroyed.

Trivia

 * Hardened clay was suggested by BlameTC.