Sadanagaite (Magnesiosadanagaite, etc.)
Current inventory: 0 gems
 

  
Sadanagaite was named to honor Professor Ryoichi Sadanaga of the Mineralogical Institute, University of Tokyo, Tokyo, Japan.

Discovered in 1980; IMA status: Valid (IMA Approved 1984)

Chemistry

Chemical Formula:

(K,Na)Ca₂(Fe²⁺,Mg,Al,Ti)₅[(Si,Al)₈O₂₂](OH)₂

Potassium Sodium Calcium Magnesium Aluminum Iron Silicate Hydroxide

Molecular Weight:

931.99 gm

Composition:

Potassium

3.15 %

K

3.79 %

K₂O

Sodium

0.62 %

Na

0.83 %

Na₂O

Calcium

8.60 %

Ca

12.03 %

CaO

Magnesium

3.91 %

Mg

6.49 %

MgO

Titanium

1.28 %

Ti

2.14 %

TiO₂

Aluminum

7.96 %

Al

15.04 %

Al₂O₃

Iron

14.98 %

Fe

19.27 %

FeO

Silicon

18.08 %

Si

38.68 %

SiO₂

Hydrogen

0.22 %

H

1.93 %

H₂O

Oxygen

41.20 %

O

100.00 %

100.21 %

= TOTAL OXIDE

Classification

Mineral Classification:

Silicates (Germanates)

Strunz 8th Ed. ID:

8/F.10-175

Nickel-Strunz 10th Ed. ID:

9.DE.15

9 : SILICATES (Germanates)
D : Inosilicates
E : Inosilicates with 2-periodic double chains, Si₄O₁₁; Clinoamphiboles

Related to:

Sadanagaite Root Name Group. Calcium Amphibole Subgroup. w(OH, F, Cl)-dominant Amphibole Group. Amphibole Supergroup. Magnesio-Sadanagaite - Sadanagaite Series.

Members of Group:

Sadanagaite Root Name Group: Ferri-fluoro-sadanagaite, Ferri-sadanagaite, Ferro-ferri-fluoro-sadanagaite, Ferro-ferri-sadanagaite, Ferro-fluoro-sadanagaite, Ferro-sadanagaite, Fluoro-sadanagaite, Potassic-chloro-sadanagaite, Potassic-ferri-sadanagaite, Potassic-ferro-chloro-sadanagaite, Potassic-ferro-ferri-sadanagaite, Potassic-ferro-sadanagaite, Potassic-sadanagaite, Sadanagaite

Varieties:

None

Synonyms:

IMA1980-027, Magnesiosadanagaite

Crystal Data

Crystallography:

Monoclinic

Crystal Habit:

Prismatic crystals, to 1 mm; as polycrystalline aggregates. 

Twinning:

None

Physical Properties

Cleavage:

Perfect on {110}

Fracture:

n/a

Tenacity:

Brittle

Moh's Hardness:

~6.0

Density:

3.30 (g/cm³)

Luminescence:

None

Radioactivity:

Barely Detectable; GRapi = 44.72 (Gamma Ray American Petroleum Institute Units)

Optical Properties

Color:

Dark brown to black; in thin section, paler with greater silicon content

Transparency:

Semi-transparent to opaque

Luster:

Vitreous

Refractive Index:

1.673 - 1.697  Biaxial ( + ) or ( - )

Birefringence:

0.024

Dispersion:

Perceptible; r > v

Pleochroism:

Strong; X = pale brown, grayish, or greenish yellow; Y = yellowish orange to light olive-brown; Z = greenish brown, light olive-brown to dark yellowish orange

Occurances

Geological Setting:

By contact metamorphism, producing banded skarns, under amphibolite to pyroxene hornfels facies conditions; from eclogites.

Common Associations:

Vesuvianite, Hercynite, Sphene, Ilmenite, Apatite (Yuge Island, Japan); Biotite, Orthoclase, subsilicic ferroan Pargasite (Nogo-Hakusan area, Japan)

Common Impurities:

Mn

Type Locality:

Kasuga mine, Kasuga-mura, Ibigawa-cho, Gifu Prefecture, Chubu Region, Honshu Island, Japan

Year Discovered:

1980 (IMA Approved 1984)

View mineral photos:

Sadanagaite Mineral Photos and Locations

Unusual Gem Categories

Black Gems, Radioactive Gems

More Information

Mindat.org
Webmineral.com

Sadanagaite is a rare silicate mineral that is a silica-poor member of the Calcium Amphibole Subgroup of minerals. Technically speaking, Sadanagaite is a subsilicic, alumina-rich, calcic amphibole. Sadanagaite is also barely radioactive due to its potassium (K) content.  Sadanagaite is actually considered a group name with over a dozen members each varying slightly in their chemical composition. The main differences between the members are in the presence, or lack of, and the amounts of, chlorine (Cl), flourine (F), iron (Fe) and potassium (K). The result of these variations are names like Ferri-fluoro-sadanagaite and Potassic-ferro-chloro-sadanagaite. Faceted gems are very rare and are opaque, dark brown to black with vitreous luster and Moh's hardness of about 6.0. The only current source of gem sized crystals is at Nusfjord, Flakstadøya Island, Flakstad, Lofoten, Nordland, Norway.

Sadanagaite was discovered in 1980 at the Kasuga mine, Kasuga-mura, Ibigawa-cho, Gifu Prefecture, Chubu Region, Honshu Island, Japan and approved by the IMA as a new mineral species in 1984. Since then, the name Sadanagaite has been given Group status and the Sadanagaite Group has been redefined twice, in the 1997 and 2012 IMA amphibole reports. Sadanagaite was named to honor Professor Ryoichi Sadanaga of the Mineralogical Institute, University of Tokyo, Tokyo, Japan.

Sadanagaite distribution: on Yuge Island, Ehime Prefecture, and in the Nogo-Hakusan area, Fukui Prefecture, Japan. At Nusfjord, Flakstadøya Island, Flakstad, Lofoten, Nordland, Norway. At the Botallack mine, St. Just, Cornwall, England. In the Oetztal, Austria.
 

  
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