Well knows as ornamental rock, often mixed with calcite , becomes rare in gem quality.
Is a Manganese Iron Magnesium Calcium Silicate, with an hardness of 5.5 -6.5 from the Mohs’s scale.
It is found in various world part, and recently also Brazil produced some nice material as the stone described here. It has some fibrous inclusions ( very rare to find flawless) but overall looks beautiful. For collectors!