R esults show that the modified cement with good durability, small expansion and low alkality can be made by use of gypsum and zeolite modifying alumina cement.
True Invisibility Cloaks, though rare, exist in this world of ours; however, the story makes it clear that Death's Cloak is of a uniquely durable nature.
Zircon is similar to quartz, both in its chemical structure and in its durability, they both stick around a long time after other minerals weather away.
While our modern concrete has the strength to hold up very tall buildings and heavy infrastructure, it cannot compete with the endurance of these ancient materials.