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GEOREF RECORD

Chiappinoite-(Y), Y (sub 2) Mn(Si (sub 3) O (sub 7) ) (sub 4) , a new layer silicate found in peralkaline syenitic ejecta from the Agua de Pau Volcano, Azores

Anthony R. Kampf and Robert M. Housley
Chiappinoite-(Y), Y (sub 2) Mn(Si (sub 3) O (sub 7) ) (sub 4) , a new layer silicate found in peralkaline syenitic ejecta from the Agua de Pau Volcano, Azores
European Journal of Mineralogy (February 2015) 27 (1): 91-97

Abstract

Chiappinoite-(Y) (IMA2014-040), ideally Y (sub 2) Mn(Si (sub 3) O (sub 7) ) (sub 4) , is a new mineral found in peralkaline syenitic ejecta from the Agua de Pau Volcano, San Miguel Island, Azores District, Portugal. It was discovered by collector Luigi Chiappino of Milan, Italy, after whom the mineral is named. It occurs as colorless, thin to thick prisms, up to 1 mm long, with blunt chisel-like terminations, and exhibits the forms {100}, {010}, {001}, {110} and {011}. Crystals are transparent with vitreous luster. The Mohs hardness is about 6 and the mineral is brittle with uneven fracture and one perfect cleavage on {001}. The measured and calculated densities are 3.09(2) and 3.073 g/cm (super 3) , respectively. Chiappinoite-(Y) is biaxial (-) and the refractive indices (white light) are alpha = 1.590(1), beta = 1.5978(10), gamma = 1.5982(10); 2V (sub meas) = 24(1) degrees and 2V (sub calc) = 25 degrees . The mineral exhibits no dispersion and is nonpleochroic. The optical orientation is X = C: , Y = B: , Z = A: . The empirical formula on 28 O apfu is (Y (sub 1.17) Ce (sub 0.18) Dy (sub 0.10) Na (sub 0.10) Nd (sub 0.09) Er (sub 0.08) La (sub 0.07) Gd (sub 0.07) Yb (sub 0.06) Sm (sub 0.03) Pr (sub 0.02) ) (sub Sigma 1.97) (Mn (super 2+) (sub 0.61) Ca (sub 0.25) Fe (super 2+) (sub 0.09) ) (sub Sigma 0.95) Si (sub 12.07) O (sub 28) . The eight strongest reflections in the X-ray diffraction pattern [d (sub obs.) in Aa (I) (hkl)] are: 9.84 (90) (002), 4.129 (52) (024), 3.977 (48) (114), 3.544 (100) (211,042,202), 3.203 (48) (222), 2.999 (71) (044,204), 2.478 (67) (310,046,206) and 2.065 (57) (multiple). The mineral is orthorhombic, Ibam, with a = 7.5549(3), b = 15.2342(5), c = 19.6418(14) Aa, V = 2260.6(2) Aa (sub 3) and Z = 4. The structure of chiappinoite-(Y) contains 3-tetrahedra-thick silicate layers consisting of sinuous batisite-like chains, above and below which are four-membered silicate rings. Eight-coordinate Y and Mn sites are located between the silicate layers. The structure is essentially identical to that of the synthetic phases PrNaSi (sub 6) O (sub 14) and NdNaSi (sub 6) O (sub 14) , except that the latter phases have an additional 12-coordinate Na site within the "cage" in the silicate layer.


ISSN: 0935-1221
EISSN: 1617-4011
Serial Title: European Journal of Mineralogy
Serial Volume: 27
Serial Issue: 1
Title: Chiappinoite-(Y), Y (sub 2) Mn(Si (sub 3) O (sub 7) ) (sub 4) , a new layer silicate found in peralkaline syenitic ejecta from the Agua de Pau Volcano, Azores
Affiliation: Natural History Museum of Los Angeles County, Mineral Sciences Department, Los Angeles, CA, United States
Pages: 91-97
Published: 201502
Text Language: English
Publisher: Schweizerbart'sche Verlagsbuchhandlung (Naegele u. Obermiller), Stuttgart, Germany
References: 15
Accession Number: 2015-067758
Categories: Mineralogy of silicates
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 7 tables
N37°46'60" - N37°46'60", W25°28'00" - W25°28'00"
Secondary Affiliation: California Institute of Technology, Division of Geological and Planetary Sciences, USA, United States
Country of Publication: Germany
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Abstract, copyright, Schweizerbart'sche Verlagsbuchhandlung. Reference includes data from GeoScienceWorld, Alexandria, VA, United States
Update Code: 201529
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