Morimotoite

Morimotoite is a titanium-bearing member of the garnet group, distinguished by tetravalent titanium and ferrous iron in its octahedral sites. It is closely related to andradite, melanite, and schorlomite, forming part of the continuum of dark, titanium-rich calcium garnets.

It is jet black to brownish black, isometric, hard, and resinous to vitreous in luster, typically forming small crystals or grains rather than gem material.

Morimotoite was described from Fuka, Japan, and named after the mineralogist Nobuo Morimoto.

Morimotoite forms in skarns and in silica-undersaturated alkaline igneous rocks where calcium, titanium, and iron are concentrated. At Fuka, Japan, it occurs in skarn developed at the contact between limestone and intruding igneous rock.

The stability of titanium-rich garnets is favored by calcium-rich, relatively reducing or titanium-saturated conditions. It is associated with other calc-silicates and, in alkaline settings, with minerals like melanite, perovskite, and titanite.

It has been reported from skarn and alkaline-rock localities in Japan, Italy, and elsewhere.

Look for jet-black, hard isometric garnet crystals with a resinous luster in skarn or alkaline igneous rock. Hardness is about 7-7.5 with a grayish streak.

Morimotoite is virtually indistinguishable by eye from melanite and schorlomite; only chemical analysis showing dominant Ti4+ and Fe2+ confirms it. Distinguish black garnets in general from magnetite (which is strongly magnetic with a black streak) and from schorl tourmaline (which is prismatic and striated).

Morimotoite has no gem or industrial use because it is opaque and dark. It is significant scientifically as one of the formally defined titanium garnet species, helping clarify the complex chemistry of dark calcium-titanium garnets.

Specimens are valued by collectors of rare garnet-group minerals. Dark garnets are sometimes loosely associated with grounding in metaphysical lore, but morimotoite has no documented properties of its own.