Formula: Mg2Al3(Si3Al)O10(OH)8
Phyllosilicate (sheet silicate), chlorite group
Crystal System: Monoclinic
Specific gravity: 2.63 to 2.68 measured, 2.653 calculated
Hardness: 2½ to 3½
Streak: White
Colour: White to light green
Solubility: Sometimes slowly decomposed by acids
Common impurities: Ti,Mn,Ca,K,H2O

Igneous environments
Sedimentary environments
Metamorphic environments
Hydrothermal environments

Sudoite is found mainly as earthy masses of microscopic crystals. It is fairly widespread in a number of geologic settings, often coexisting with other fine-grained minerals (R&M 85.4.324). It is found disseminated in hematite ore, probably of hydrothermal origin, as as an authigenic mineral in aeolian sandstones, and in low-grade metamorphic assemblages (Mindat).


At Ottré, Vielsalm, Luxembourg, Wallonia, Belgium, sudoite occurs in a low-grade metamorphic assemblage (HOM, R&M 85.4.324).

At the Kesselberg area, Triberg im Schwarzwald, Schwarzwald-Baar-Kreis, Freiburg, Baden-Württemberg, Germany, sudoite is formed by hydrothermal alteration of a quartz porphyry tuff (AM 48.214).

The type locality is the Knollenberg Keuper formation, Lützelbach, Plochingen, Esslingen, Stuttgart Region, Baden-Württemberg, Germany.

At Biesenrode, Mansfeld, Wippra Metamorphic Zone, Saxony-Anhalt, Germany, sudoite is associated with quartz, carpholite, manganoan garnet and hematite (HOM).

At Itaya, Gyogo Prefecture, Japan, sudoite is associated with pyrophyllite, diaspore, mica and böhmite (HOM).

At the Tracy Mine, Negaunee, Marquette county, Michigan, USA, sudoite is a constituent of hematite iron ore presumed to be of hydrothermal origin (HOM, R&M 85.4.324).

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