The Rutile Group of minerals includes some important metal ores and some rare minerals. Rutile and cassiterite are the most important ores of titanium and tin respectively. Pyrolusite is an important ore of manganese, although not the most important. Other members of the group are much more scarce.
Members of the group have the general formula MO2. The M can be any of several metal ions with a positive 4 charge. The commoner members have lead, titanium, tin, and manganese, but germanium, silicon and tellurium also are found in the minerals of this group.
The Rutile Group minerals are tetragonal (meaning they have one four fold axis) with a 4/m 2/m 2/m symmetry. The structure is composed of parallel chains of octahedrons composed of the M ion surrounded by six oxygens. It is the parallel chain structure that produces the prismatic crystal habit typical of this group. The octahedron chains are arranged with the octahedrons on their "sides" and sharing opposing edges with other octahedrons. The four fold symmetry is the result of the square void created between the chains.
Another important characteristic of the Rutile Group is its ease of twinning. All members that produce crystalline forms can easily twin at a 60 degree angle and form "elbow twins" and cyclic twins of six or eight components. The twins of rutile and cassiterite are considered classics.
The Halide mineral