gems, spinel, Afghanistan, Tajikistan, balas ruby, Kuh-i-Lal, Pamir

The Kukhi-Lal noble spinel deposit formed during regional metamorphism of granulite and amphibolite facies in the Precambrian and epidote-amphibolite facies in the Cenozoic. In all of its constituent mineral associations, cavities are developed, which are divided into two groups: the 1st group has a slit-like shape, its length is tens of cm and the degree of disclosure is up to 10 cm; the 2nd group has isometric shapes, its volume is up to 8 cm³, with newly formed minerals (chlorite, dolomite, aragonite) growing from the walls. The formation of the cavities is related to the regressive stage of the 2nd metamorphism cycle (temperature ranges are 700° to 660°C, and pressure ranges are 800 to 350 MPa). The formation of the cavities is regarded as a stage in the development of the Kukhi-Lal deposit.