Sinhalite is a mineral with a hardness of 7 out of 10 on the Mohs scale of mineral hardness [?]. These Orthorhombicly structured gems are made of magnesium aluminum iron borate, their full chemical compound being Mg(Al,Fe)BO4.
Sinhalite is a magnesium aluminum borate, and is most commonly found as transparent honey-yellow to brown grains or pebbles with an orthorhombic crystal system.
It also appears as pale yellowish, yellow, brown, greenish-brown to black.
It occurs in contact metamorphic rocks that are rich in boron, among gneiss or granite where limestones are being replaced through contact with magmatic rock. But most gem sinhalite is found as alluvial pebbles, carried by flowing water from upstream down to riverbeds. It exhibits brown, green-brown colors when light is passed through it.
It only used to be found in Sri Lanka, but it also began to be found from Myanmar (Burma) since 1958. A transparent golden brown chatoyant variety with a silver eye was found from its main source, Sri Lanka.
Aside from Sri Lanka and Myanmar, it is also found in Tanzania and the USA.
Before 1952, when it was found to be a unique gem altogether, sinhalite was known as brown peridot or brown chrysolite because it has similar properties and refractive index to peridot. It is still a rare mineral today, and for years was known only from the gem gravels of Sri Lanka, thus taking its name from "sinhala" (Ceylon) in Sanskrit, the country's old name.
Sinhalite is rarely cut as faceted gems. When faceted as a gem, it resembles yellow or brown chrysoberyl.