Minnesotaite is an iron

silicate mineral Silicate minerals are rock-forming minerals made up of silicate groups. They are the largest and most important class of minerals and make up approximately 90 percent of Earth's crust. In mineralogy, silica (silicon dioxide, ) is usually consid ...

with formula: (Fe²⁺,Mg)₃Si₄O₁₀(OH)₂. It crystallizes in the

triclinic crystal system 180px, Triclinic (a ≠ b ≠ c and α ≠ β ≠ γ ) In crystallography, the triclinic (or anorthic) crystal system is one of the 7 crystal systems. A crystal system is described by three basis vectors. In the triclinic system, the crystal i ...

and occurs as fine needles and platelets with other silicates. It is isostructural with the pyrophyllite-

talc Talc, or talcum, is a clay mineral, composed of hydrated magnesium silicate with the chemical formula Mg3Si4O10(OH)2. Talc in powdered form, often combined with corn starch, is used as baby powder. This mineral is used as a thickening agent a ...

mineral group.

Occurrence

Minnesotaite was first described in 1944 for occurrences in the

banded iron formation Banded iron formations (also known as banded ironstone formations or BIFs) are distinctive units of sedimentary rock consisting of alternating layers of iron oxides and iron-poor chert. They can be up to several hundred meters in thickness ...

s of northern

Minnesota Minnesota () is a state in the upper midwestern region of the United States. It is the 12th largest U.S. state in area and the 22nd most populous, with over 5.75 million residents. Minnesota is home to western prairies, now given over to ...

for which it was named. Co-type localities are in the Cuyuna North Range,

Crow Wing County Crow Wing County is a County (United States), county in the East Central part of the U.S. state of Minnesota. As of the 2020 United States census, 2020 census, the population was 66,123. Its county seat is Brainerd, Minnesota, Brainerd. The coun ...

and the Mesabi Range in St. Louis County. It occurs associated with

quartz Quartz is a hard, crystalline mineral composed of silica ( silicon dioxide). The atoms are linked in a continuous framework of SiO4 silicon-oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall chemical ...

siderite Siderite is a mineral composed of iron(II) carbonate (FeCO3). It takes its name from the Greek word σίδηρος ''sideros,'' "iron". It is a valuable iron mineral, since it is 48% iron and contains no sulfur or phosphorus. Zinc, magnesium and ...

, stilpnomelane,

greenalite Greenalite is a mineral in the kaolinite- serpentine group with the chemical composition (Fe2+,Fe3+)2-3Si2O5(OH)4.Sleep N.H., Bird D.K. (2007): Niches of the pre-photosynthetic biosphere and geologic preservation of Earth’s earliest ecology. Ge ...

and

magnetite Magnetite is a mineral and one of the main iron ores, with the chemical formula Fe2+Fe3+2O4. It is one of the oxides of iron, and is ferrimagnetic; it is attracted to a magnet and can be magnetized to become a permanent magnet itself. With th ...

.Gruner, John W., ''The Composition and Structure of Minnesotaite, a Common Iron Silicate in Iron Formations,'' American Mineralogist, 1944, 29, 363-372
/ref> In addition to the low grade

metamorphic Metamorphic rocks arise from the transformation of existing rock to new types of rock in a process called metamorphism. The original rock (protolith) is subjected to temperatures greater than and, often, elevated pressure of or more, causi ...

banded iron formations it has also been reported as an alteration mineral associated with sulfide bearing veins.

References

{{Reflist Phyllosilicates Triclinic minerals Minerals in space group 2