Formula: Al2(SiO4)(F,OH)2 Orthorhombic Description: Topaz from the Nine Mile Pluton near Wausau in Marathon County, Wisconsin. Scanning electron microscope image. (Photo by Al Falster.) Topaz forms in granitic pegmatites, in cavities in rhyolitic volcanic rocks and in residual …
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Todorokite
Formula: (Ca,K,Na,Mg,Ba,Mn)(Mn,Mg,Al)6O12.3H2O Monoclinic Description: Todorokite is soft sooty brown, gray to black mineral formed as a result of the alteration of other manganese minerals or as a precipitate from surficial waters. Todorokite is reported as a …
Titanite
Formula: CaTiSiO5 Monoclinic Description: Titanite is a common accessory mineral usually found as tiny grains in many different rocks. It is common in plutonic igneous rocks such as granite, diorite and syenite. Titanite also is a common …
Thorogummite
Formula: (Th,U)(SiO4)1-x(OH)4x Tetragonal Description: Thorogummite is formed by the alteration of other thorium-rich minerals, such as thorite. IMA currently lists its status as a species as “doubtful.” MARATHON COUNTY: Much of the thorite found in the pegmatites of …
Thorite
Formula: (Th,U)SiO4 Tetragonal Description: Thorite is a rare mineral found in pegmatites and hydrothermal deposits. MARATHON COUNTY: Thorite is found in the pegmatites associated with the amphibole syenites of the Stettin pluton. Some grains and clusters may be …
Thomsonite-Ca
Formula: NaCa2Al5Si5O20.6H2O Orthorhombic Description: Thomsonite-Ca is a member of the zeolite group often found in radiating clusters of varying color in the amygdules of volcanic rocks.IRON COUNTY: Thomsonite-Ca occurs abundantly in outcrops of the Porcupine volcanics along …
Thalenite-(Y)
Formula: Y3Si3O10(OH) Monoclinic Description: Thalenite-(Y) is a rare mineral found as pinkish, greenish or brownish grains in complex pegmatites. MARATHON COUNTY: Thalenite-(Y) has been documented as occurring as rare grains in pegmatites in the Koss Pit, a …
Tetrahedrite-tennantite
Formula: (Cu,Fe,Ag,Zn)12(Sb,As)4S13 Isometric Description: Tetrahedrite forms a solid solution series with tennantite and freibergite in moderate to low temperature hydrothermal deposits. DOUGLAS COUNTY: Irving (1882) reports finding tetrahedrite in “small quantities in traverse veins in copper-bearing rocks”. This …
Tenorite
Formula: CuO Monoclinic Description: Tenorite is a black massive mineral found in the oxidized portions of copper deposits where it is associated with other secondary minerals such as cuprite, malachite, azurite, goethite and hematite. It usually …
Tapiolite Series
Formula: (Fe,Mn)(Ta,Nb)2O6 – (Mn,Fe)(Ta, Nb)2O6 Tetragonal Description: Tapiolite-(Fe), Koss Pit, near Wausau, Marathon County, Wisconsin (Photo by Al Falster.) A series exists between ferri-tapiolite and manganotapiolite. These rare minerals are found in complex granite pegmatites. MARATHON COUNTY: A member of …