These are inclusions buried within emerald. Em­erald is a member of the beryl family, its chemical composition being beryllium aluminium silicate.

Ruby is defined as crystalline aluminium oxide, called corundum, with traces of the chemical element chromium, which is responsible for its red colour.

Defined as crystalline aluminium oxide Al2O3, called corundum, with traces of the elements iron and titanium, a delicate balance of the right chemic elements is required to supply the growing crystal with the ingredients that finally lend it an appealing blue colour.