Final answer:
Curved growth striae in some synthetic rubies are caused by the constraints of the host lattice and the growth process of the crystal.
Step-by-step explanation:
The curved growth striae in some synthetic rubies are caused by the constraints of the host lattice. In rubies, the Cr-O distances are relatively short due to the Al2O3 composition of the host lattice. This results in increased d orbital-ligand interactions and a large absorption coefficient (A). The curved growth striae occur as a result of the growth process of the synthetic ruby, where the crystal lattice grows in a curved manner, causing the growth lines to be curved.