Giza Limestone is an Egyptian crafting material needed for rare items and Egyptian 20-slot warehouse King Tut's Attic. It is itself rare, and can be bought from other players, or slowly accumulated (5 pieces per 12-hour refresh mission) by a repeatable quest at the Nubian Expedition called Trade for Giza Limestone.
Used in the following blueprints
Medium Egyptian Residence - 1 per
Large Egyptian Residence - 2 per
King Tut's Attic - 10 per
Small Obelisk - 1 per
Obelisk - 2 per
Large Obelisk - 3 per
Small Step Pyramid - 3 per
Old Temple - 3 per
Mystic Temple - 3 per
Can be stacked 100 units per inventory space.