Tunisite, a new carbonate from Tunisia

Zdenek Johan; Pavel Povondra; Ervin Slansky

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Research Article| February 01, 1969

Tunisite, a new carbonate from Tunisia

Zdenek Johan;

Zdenek Johan

Geological Institute of the Czechoslovak Academy of Sciences, Prague, Czechoslovakia.

¹Present address: B. R. G. M., B. P. 818, 45-0rleans-La Source, France.

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Pavel Povondra;

Pavel Povondra

Geological Institute of the Czechoslovak Academy of Sciences, Prague, Czechoslovakia.

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Ervin Slansky

Geological Institute of the Czechoslovak Academy of Sciences, Prague, Czechoslovakia.

²Present Address: Department of Geology, Kuwait University, Kuwait.

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Author and Article Information

Zdenek Johan

Geological Institute of the Czechoslovak Academy of Sciences, Prague, Czechoslovakia.

¹Present address: B. R. G. M., B. P. 818, 45-0rleans-La Source, France.

Pavel Povondra

Geological Institute of the Czechoslovak Academy of Sciences, Prague, Czechoslovakia.

Ervin Slansky

Geological Institute of the Czechoslovak Academy of Sciences, Prague, Czechoslovakia.

²Present Address: Department of Geology, Kuwait University, Kuwait.

Publisher: Mineralogical Society of America

Received: 11 Jun 1968

Accepted: 10 Oct 1968

First Online: 06 Jul 2018

Online ISSN: 1945-3027

Print ISSN: 0003-004X

Mineralogical Society of America

American Mineralogist (1969) 54 (1-2): 1–13.

Abstract

Tunisite, NaHCa₂Al₄[(CO₃)₄(OH)₁₀] is a new carbonate found at the Pb – Zn deposit, Sakiet Sidi Youssef, Tunisia. It occurs in fine-grained white aggregates or in small tabular crystals associated with pyrite, marcasite, sphalerite and calcite in hydrothermal veins.

The new mineral is tetragonal; D⁷_4h – P4/nmm; a = 11.22 ± 0.01, c=6.582±0.001 Å, c/a=0.5866; V = 828.6 Å³, cell contents: 2{NaHCa₂Al₄[(CO₃)₄(OH)₁₀.). The strongest lines in the X-ray powder photograph are: 5.615 (10), 2.592 (9), 3.551 (8), 3.288 (7), 2.526 (7) Å.

Tunisite is colorless. H = 4,5; ρ 2.51±0.02 (meas.), 2.48 (calc.). Basal and prismatic cleavage very good. Optically uniaxial (+), ω= 1.573 ± 0.001, ϵ= 1.599 ± 0.001.

The chemical analysis: Na₂O 4.77, K₂O 0.35, CaO 18.08, A1₂O₃ 32.56, CO₂ 28.66, H₂O⁺ 15.04, H₂O^– 0.51, Σ 99.97 wt.%. DTA shows a strong endothermic peak at 440° (escape of 8CO₂+7H₂O) and an exothermic peak at 850° (formation of new crystalline phases and escape of 2H₂O). IR spectrum shows absorption bands at 680 s, 850 s, 1155 s, 1530 vs, 1725 w, 1860 vw, 1920 w, 2330 vw, 2650 w, 3500 s cm⁻¹.