The sole gem marialite deposit in China is located at the western foot of Mount Muztagh,Akto County, Xinjiang, which is tectonically belongs to the Central Famirs fold belt. Gem marialite orebodies occur as veins along a structural shetter zone in the Proterozoic garnet-biotite-plagioclase gneiss. There is an obvious rock zonation from the middle to both sides of the structural shatter zone, generally from marialite orebody through diopside-felsite,biotite-albitite to the host Proterozoic rocks. This deposit was formed by hydrothermal metaso-matism。 Mainly in association with albite，marialite assumes tetragonal prism form，generally (0. 5-1 .2)×(1-2)cm in size with a few grains smaller than 0 .5 cm; transparent to translucent (attributed to the existence of gas-liquid inclusions) in hand specimens, and light to dard purple in color. Under mioroscope, it is colorless, optically uniaxial negative, with measured refractive indices No=1.541, Ne=1.537. Measured density 2.561 g/cm3;Moh’s hardness 5.5-6. X-ray powder diffraction data: tetragonal, I 4/ m，a0=12.0(3)，c0= 7.53 (4)A, V=1084.3A3.wet chemical analysis and electron microprobe analysis give the composition of marialite as follows(in wt %):Na2O 11.37-11.60, A1203 18.94-19.98, SiO2 60.51-62.09, K201.20-1.88, Ca01.81-2.02, Cl 4.10-5.17, F<0.1, H20+ 0.27,suggesting that it is the Na end member of scapolite. The composition of scapolite has been traditionally expressed in term of Ma and Me ( Me=100×( Ca+Sr)/(Na+K+Ca+Sr)(Shaw, 1960;Ma= 100一Me)，and the Ma and Me values of marialite from this deposit are Ma= 93.5-91.9 and Me=6.5-8.1. Almost all naturally occurring scapolites fall in the compositional range Ma 20-80 ( Orville, 1975 ).Pure marialite does not occur in nature and 80%Ma is the maximum attained ( Shaw, 1960 ).Ma of the marialite from this deposit is higher than 91, indicating that the mineral is a rare type in ature. Marialite from this deposit can be used as gem and can be cut into facet or cabochon,which has distinct chatoyancy. Research shows that the color of marialite is mainly caused by color center.