Just like other regular quartz only this contains Brookite.

Brookite is a rare, naturally occurring mineral and one of the three main forms of titanium dioxide, along with rutile and anatase. It's known for its metallic luster and distinctive tabular or prismatic shape.

Brookite is typically brown, but can also be black, reddish-brown, or yellowish. The color and clarity of brookite crystals depends on their iron content.