Låvenite (original) (raw)

Formula:

Na2Ca2Mn2Zr2(Si2O7)2O2F2

Formula from Dal Bo et al. (2022).

Colour:

Colorless to brownish-yellow, brown, brownish-red, orange-brown.

Specific Gravity:

3.4 - 3.55

Crystal System:

Monoclinic

Name:

Named for the type locality, Låven island, Langesundsfjord, Norway by the Norwegian geologist and mineralogist Waldemar Christopher Brøgger (10 November 1851 – 17 February 1940). In 1875, Brøgger and Hans Reusch had found, in a nepheline syenite pegmatite at Låven, a mineral first assumed by Brøgger to be mosandrite (Brøgger 1878). Later he recognized it as a new mineral and gave a preliminary description (Brøgger 1885).
A more detailed description was published by Brøgger (1890). The crystal structure was solved by Mellini (1981) and refined on samples from Lovozero, Russia by Simenov and Belov (1960) and from Los Archipelago, Guinea by Biagoni et al. (2012).
Dal Bo et al. (2022) reviewed the data on låvenite in their paper on the wöhlerite group minerals.

A sorosilicate belonging to the wöhlerite group. Forms a solid solution-series with normandite, where låvenite is the Zr- and normandite the Ti-endmember.

May be the Mn analogue of UM2003-34-SiO:CaFFeMnNaNbTiZr; and also the Mn analogue of madeiraite (?).

The structure of Låvenite structure can be described as four-columns wide "octahedral" walls interconnected by corner-sharing and via disilicate groups. Structural and chemical data indicate cationic substitution on the four X sites. X2 and X4, which are the largest sites in the "octahedral" wall, are dominated by Ca and Na, respectively. The site X3 is dominated by Mn2+ and X1, the smallest site, is dominated by Zr (Dal Bo et al. 2022)

Approved, 'Grandfathered' (first described prior to 1959)

IMA Formula:

(Na,Ca)4(Mn2+,Fe2+)2(Zr,Ti,Nb)2(Si2O7)2(O,F)4

Transparency:

Transparent, Translucent

Colour:

Colorless to brownish-yellow, brown, brownish-red, orange-brown.

Streak:

Yellowish-white; pale brown

Cleavage:

Distinct/Good
Good on {100}

Fracture:

Irregular/Uneven

Density:

3.4 - 3.55 g/cm3 (Measured) 3.498 g/cm3 (Calculated)

RI values:

_n_α = 1.670 _n_β = 1.690 _n_γ = 1.720

2V:

Measured: 40° to 70°, Calculated: 80°

δ = 0.050

Image shows birefringence interference colour range (at 30µm thickness)
and does not take into account mineral colouration.

Dispersion:

r < v perceptible

Optical Extinction:

Y = b; Z ∧ c = -20°.

Comments:

X = colorless, pale yellow; Y = colorless, pale greenish yellow; Z = very pale yellow, orange to brownish yellow.

Comments:

Absorption: Z > Y > X.

Crystal System:

Monoclinic

Class (H-M):

2/m - Prismatic

Cell Parameters:

a = 10.83(1) Å, b = 9.98(1) Å, c = 7.174(5) Å
β = 108.1°

Ratio:

a:b:c = 1.085 : 1 : 0.719

Unit Cell V:

737.02 ų (Calculated from Unit Cell)

Morphology:

Crystals prismatic parallel to [100] or tabular. Also acicular radial, fibrous, granular, or massive. Forms include {100}, {110}, {111}, {101}.

Twinning:

Polysynthetic on {100}.

General Appearance of Type Material:

Chest-nut brown to yellow elongated, prismatic crystals.

Place of Conservation of Type Material:

Naturhistoriska Riksmuseet, Stockholm, Sweden inventory nr. 531056

Geological Setting of Type Material:

nepheline syenite pegmatite

Associated Minerals at Type Locality:

- This locality has map coordinates listed. - This locality has estimated coordinates. ⓘ - Click for references and further information on this occurrence. ? - Indicates mineral may be doubtful at this locality. - Good crystals or important locality for species. - World class for species or very significant. (TL) - Type Locality for a valid mineral species. (FRL) - First Recorded Locality for everything else (eg varieties). Struck out - Mineral was erroneously reported from this locality. Faded * - Never found at this locality but inferred to have existed at some point in the past (e.g. from pseudomorphs).

All localities listed without proper references should be considered as questionable.