Hejtmanite (original) (raw)

Formula:

Ba2Mn2+4Ti2(Si2O7)2O2(OH)2F2

Colour:

Brownish to golden yellow

Specific Gravity:

3.97 - 4.06

Name:

Named in honour of Prof. RNDr. Bohuslav Hejtman (12 August 1911 Stranná u Kamenice nad Lipou - 18 September 2000 Praha), professor of petrology at Charles University in Prague, Czech Republic.

The Mn analogue of bafertisite (redefined as so basing on the Mbolve Hill material).

Previously reported to be monoclinic, which was proved wrong.

Chemistry is somewhat similar to that of perraultite. Compare UM1989-33-SiO:BaHMnTi.

Hejtmanite belongs to a group of titanosilicates built of TS (titanosilicate) and I (intermediate) blocks. In this group the TS block consists of HOH sheets, with H standing for heteropolyhedral sheets (penta- and hexacoordinated), and O for central octahedral (trioctahedral) sheet (Sokolova, 2010).
Hejtmanite is a Group-II TS-block mineral, which indicates that the (Ti+Nb) to (Si2O7) ratio is 2:2. In hejtmanite the O sheet consists of five hexacoordinated MO sites occupied mainly by Mn, surrounded by O or OH. The H sheet has (1) two hexacoordinated MH sites (mainly Ti, surrounded by O or F), and (2) four tetrahedral silicon sites. The I block comprises a layer of [12]Ba atoms, that reside within two AP(1,2) sites. Ba is surrounded by O or F. Four (XO) sites equal to two (XO M) and two (XO A) sites, corresponding to O2(OH)2 (Sokolova et al., 2016).

RI values:

_n_α = 1.814 _n_β = 1.846 _n_γ = 1.867

2V:

Measured: 76° to 76.8°, Calculated: 76°

δ = 0.053

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

Optical Extinction:

X = b; Y ∧ c = 37.9°; Z ∧ a = 15.9°.

Comments:

X = light yellow-green; Y = dark golden yellow; Z = light yellow.

Comments:

Absorption: Y > Z = X.

Class (H-M):

1 - Pinacoidal

Cell Parameters:

a = 10.716(2) Å, b = 13.795(3) Å, c = 11.778(2) Å
α = 90.07(3)°, β = 112.24(3)°, γ = 90.03(3)°

Ratio:

a:b:c = 0.777 : 1 : 0.854

Comment:

Space group setting is C-1

General Appearance of Type Material:

Prismatic or platy crystals up to 1 mm long enclosed in manganoan arfvedsonite.

Place of Conservation of Type Material:

Charles University, Praha, Czech Republic (cotype).
National Museum, Praha, Czech Republic (cotype).

Geological Setting of Type Material:

A system of young segregation veins of manganoan arfvedsonite cutting foliated alkali granite and syenite.

Associated Minerals at Type Locality: