Mineral Species: Boulangerite and Calcite 

Chemical Formula: Pb5Sb4S11

Chemical Name: Lead Antimony Sulfide

Mineral Class: Sulphosalt

Mineral Notes: Boulangerite is one of a few sulfide minerals that form hair-like fibrous crystals. The aggregates may be so thick as to entirely cover a matrix or single needles that are lodged between other minerals. Jamesonite and Millerite are two other sulfides that form similar crystals and can be mistaken for Boulangerite. However, Millerite is yellow and Jamesonite has brittle crystals. Boulangerite is a Sulfosalt, a type of Sulfide where Antimony acts like a metal and occupies a position where it is bonded to Sulphur. Boulangerite and Jamesonite are called feather ores. A variety of Boulangerite is called "plumosite" due to its feathery tufts and was once believed to be a different mineral.

Description: A very interesting specimen. One side is formed of small green-yellow Calcite crystals having a prismatic habit. The front side is also formed from this Calcite but this time the Calcite is blue-grey due to the inclusions of Boulangerite. There is a very sharp boundary between the two, along the axis of the specimen, showing a very sharp transition between two sets of mineralising solutions. Close inspection of the Boulangerite shows small tuft-like crystals enclosed in the Calcite.

Location: Herzsabanya, Romania.