Aenigmatite

Discovered in 1865; IMA status: Valid (pre-IMA; Grandfathered)

Chemistry

Chemical Formula:

Na₂Fe₅²⁺Ti(Si₆O₁₈)O₂

Sodium Iron Titanium Silicate Oxide

Atomic Number:

1,717.59 gm

Molecular Weight:

127.60 gm

Composition:

Sodium

4.99 %

Na

6.73 %

Na₂O

Calcium

0.77 %

Ca

1.08 %

CaO

Magnesium

0.65 %

Mg

1.08 %

MgO

Zirconium

0.05 %

Zr

0.07 %

ZrO₂

Titanium

5.85 %

Ti

9.77 %

TiO₂

Manganese

1.28 %

Mn

1.65 %

MnO

Aluminum

1.01 %

Al

1.90 %

Al₂O₃

Zinc

0.04 %

Zn

0.05 %

ZnO

Iron

29.95 %

Fe

35.76 %

FeO /  3.07 % Fe₂O₃

Silicon

18.15 %

Si

38.83 %

SiO₂

Oxygen

37.26 %

O

100.00 %

99.99 %

= TOTAL OXIDE

Classification

Mineral Classification:

Silicates (Germanates)

Strunz 8th Ed. ID:

8/F.14-20

Nickel-Strunz 10th Ed. ID:

9.DH.40

9 : SILICATES (Germanates)
D : Inosilicates
H : Inosilicates with 4-periodic single chains, Si₄O₁₂

Related to:

Aenigmatite Group. Sapphirine Supergroup. Aenigmatite-Wilkinsonite Series.

Members of Group:

Aenigmatite Group: Aenigmatite, Krinovite, Kuratite, Wilkinsonite 

Varieties:

None

Synonyms:

Cossyrite, Cosyrite, ICSD 15283, Kölbingite, PDF 46-1473

Crystal Data

Crystallography:

Triclinic - Pinacoidal

Crystal Habit:

Crystals poorly developed, prismatic, to 8 cm; as irregular segregations.

Twinning:

By rotation ⊥ (011) or about [010] of the pseudomonoclinic cell; polysynthetic 

Physical Properties

Cleavage:

Good on {010}, {100}

Fracture:

Irregular/Uneven

Tenacity:

Brittle

Moh's Hardness:

5.5 - 6.0 

Density:

3.81 (g/cm³)

Luminescence:

None

Radioactivity:

Not Radioactive

Optical Properties

Color:

Velvet-black; in thin section, reddish brown to black

Transparency:

Translucent to opaque

Luster:

Vitreous to greasy

Refractive Index:

1.780 - 1.900  Biaxial ( + )

Birefringence:

0.090 - 0.100

Dispersion:

Very strong; r < v

Pleochroism:

X = yellow brown; Y = red-brown; Z = dark brown to black

Occurances

Geological Setting:

A primary constituent in sodium-rich alkalic volcanics, pegmatites, and other silica-poor igneous rocks.

Common Associations:

Aegirine, Augite, Riebeckite, Arfvedsonite, Hedenbergite, Fayalite, Ilmenite

Common Impurities:

Al, Mn, Mg, Ca, K, Cl

Type Locality:

• Kangerluarsuk Fjord (Kangerdluarssuq Fjord), Ilímaussaq complex, Narsaq, Kujalleq, Greenland
• Naujakasik (Naajakasik), Tunulliarfik Fjord (Tunugdliarfik), Ilímaussaq complex, Narsaq, Kujalleq, Greenland

Year Discovered:

1865

View mineral photos:

Aenigmatite Mineral Photos and Locations

More Information

Mindat.org
Webmineral.com

Aenigmatite is a rare inosilicate mineral containing titanium, that is a member of the Aenigmatite Group of minerals that includes Aenigmatite, Krinovite, Kuratite and Wilkinsonite. Aenigmatite is primarily found in peralkaline volcanic rocks, pegmatites, and granites as well as silica-poor intrusive rocks. It was first described and named in 1865 by German mineralogist Johann Friedrich August Breithaupt (1791-1873) from an occurrence in the Ilimaussaq intrusive complex of southwest Greenland. The name Aenigmatite is from the Greek word αίνιγμα (aenigma), meaning a riddle, in allusion to the uncertain chemical composition of the mineral.

Aenigmatite is typically opaque, velvet-black in color with vitreous to greasy luster and often associated with bronze-brown Astrophyllite crystals. Faceted gems are very rare. Cabochons are somewhat more common but usually collected for their flashy bronze Astrophyllite crystals and the secondary black Aenigmatite crystals, if present, are not even mentioned.

In addition to the localities listed below, Aenigmatite was also reported from the Kaidun meteorite, possibly a Mars meterorite, which landed on a Soviet military base near what is now Al-Khuraybah in Yemen on December 3, 1980.

Aenigmatite distribution: notable studied occurrences include: at Naujakasik, near the Tunugdliarfik Fjord, and on the Kangerdluarssuk Plateau, in the Ilímaussaq intrusion; from Narssârssuk; and elsewhere in Greenland. In the Khibiny and Lovozero massifs, Kola Peninsula, Russia. At Sandefjord, Norway. From Cuddua Mida, Sicily, Italy. In the USA, from Granite Mountain, near Little Rock, Pulaski County, Arkansas, and Santa Rosa, Sonoma County, California. In Australia, from Warrumbungle volcano, Nandewar volcano, and the Mt. Warning complex, New South Wales; and the Peak Range Province, Queensland. From Logan Point quarry, Dunedin volcano, New Zealand.

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