The chemical formula of mineral Carrollite is indicated by the formula Cu(Co,Ni)2S4. It is also found in hydrothermal vein deposits. This mineral is most commonly found in the USA, in the Patapsco mine, Finksburg, and the Mineral Hill mine, Sykesville, Carroll Co., Maryland. Carrollite was named for its occurrence in Carroll Co., Maryland, USA. Mineral Carrollite is known to crystallize in the isometric system of crystal formation. In optical mineralogy, this isometric crystal system comprises crystals having three axes, all of which are perpendicular to one another and all are found equal in lengths. Carrollite is usually found showing indistinct clevage when evaluated with the aid of petrographic polarizing microscopes used in the field of optical mineralogy. Carrollite is most commonly found colored gray, copper red, light gray, or steel in hand sample. Carrollite is most commonly found showing density measure ranging from 4.5 to 4.8 grams per cubic centimeters, with an average of 4.65. Most crystals of mineral Carrollite are found opaque in appearance. Carrollite is also found showing conchoidal fractures developed in brittle materials characterized by smoothly curving surfaces, similar to quartz. The hardness measure of mineral Carrollite is usually found ranging from 4.5 to 5.5 when evaluated using the Mohs scale method. Carrollite is also found exhibiting metallic luster in reflected light of polarizing microscopes. Carrollite is found to be not radioactive.