Underlying appearance: ivory, bone, pale warm limestone, chalk white. Apparent darkness/warmth depends on grime, moisture, age and lighting.
Known properties vary by source/height: unusually light, luminous, hot, cold, buoyant/floating. Not exhaustive. Amended D-328 Also corrosive (poison, rot) and charged (electrical discharge).
HARD CANON: medieval human tooling cannot meaningfully reshape Tower stone. Humans use pieces already broken from the Tower.