Sudoite

Sudoite is a mineral from the chlorite group. It was named after Toshio Sudo (1911-2000), professor of mineralogy at the University of Tokyo, in Japan, and a pioneer of clay science.^[3] The mineral tosudite also bears his name. It was approved as a valid species by the International Mineralogical Association in 1966.

Sudoite
General
Category	Chlorite_group
Formula	Mg2Al3(Si3Al)O10(OH)8
Crystal system	Monoclinic
Identification
Color	White to light green
Mohs scale hardness	2.5–3.5
Luster	pearly, dull
Refractive index	nα = 1.581 à 1.583 nβ = 1.584 à 1.589 nγ = 1.591 à 1.601
Birefringence	biaxial (-) ; δ = 0.010 to 0.018 2V = 64 to 70° (measured) 2V = 68 to 72° (calculated)
References	[1][2]

Characteristics

Sudoite is a clay mineral with chemical formula defined as Mg₂Al₃(Si₃Al)O₁₀(OH)₈. It has a monoclinic crystal system. Its hardness on the Mohs scale is between 2.5 and 3.5.

Classification

Following the Nickel–Strunz classification, it is contained in the "09.EC.55" group:

Members of the 9.EC.55 group

Mineral	Formula	Symmetry group	Space group
Baileychlore	(Zn,Al) 3[Fe 2Al][Si 3AlO 10](OH) 8	1 or 1	C1 or C1
Borocookeite	Li 1+3xAl 4-x(BSi 3)O 10(OH,F) 8 (x ≤ 0,33)	2/m	C2/m
Chamosite	(Fe,Mg,Fe) 5Al(Si 3Al)O 10(OH,O) 8	2/m	C2/m
Clinochlore	(Mg,Fe) 5Al(Si 3Al)O 10(OH) 8	2/m	C2/m
Cookeite	LiAl 4(Si 3Al)O 10(OH) 8	1, 2 or 2/m	C1, C2 or Cc
Donbassite	Al 2[Al 2,33][Si 3AlO 10](OH) 8	2/m	C2/m
Franklinfurnaceite	Ca(Fe,Al)Mn 4Zn 2Si 2O 10(OH) 8	2	C2
Glagolevite	NaMg 6[Si 3AlO 10](OH,O) 8·H 2O	1	C1
Gonyerite	Mn 3[Mn 3Fe][(Si,Fe) 4O 10](OH,O) 8		unknown
Nimite	(Ni,Mg,Fe) 5Al(Si 3Al)O 10(OH) 8	2/m	C2/m
Odinite	(Fe,Mg,Al,Fe,Ti,Mn) 2,5(Si,Al) 2O 5(OH) 4	m	Cm
Orthochamosite	(Fe,Mg,Fe) 5Al(Si 3Al)O 10(OH,O) 8		unknown
Pennantite	Mn 5Al(Si 3Al)O 10(OH) 8	2/m	C2/m
Sudoite	Mg 2(Al,Fe) 3Si 3AlO 10(OH) 8	2/m	C2/m

Formation

It has been first discovered in the Knollenberg Keuper formation, in the village of Plochingen, Stuttgart Region (Baden-Württemberg, Germany).^[4] Despite being an unlikely mineral, it has been described in every continent but Antarctica and Oceania. It is found mainly in hydrothermal or high-pressure/low-temperature (HP/LT) metamorphism contexts^[5][6][7]

Use

This mineral has been used as gemstone for the production of personal ornaments, beads and pendants, during the Early Ceramic Age (500 BC – 500 AD), in the Lesser Antilles.^[8] The precise source of such formation of sudoite allowing to carve artifacts in rather large blocks remain unknown.