The primary mineral component of bone. It has the chemical formula of 3Ca3(PO4)2·Ca(OH)2 and in crystal form is a needle-shaped crystal which is arranged with other needles in a rosette. It melts above 1100°C and cannot be dissolved in water. A form of the mineral is used by molecular biologists in certain column chromatography lab techniques to separate single-stranded nucleic acids from double-stranded ones (the mineral tends to hang on to the double-stranded molecules while letting the single-stranded ones through the column unimpeded), or to separate different proteins. "Hydroxyapatite" also applies to similar minerals which have Ba (barium) or Sr (strontium) in the place of the Ca (calcium) atoms. These minerals are found in deposits of phosphorite and in biological tissue.