Ferriakasakaite-(La) and ferriandrosite-(La): new epidote-supergroup minerals from Ise, Mie Prefecture, Japan

Abstract

The new REE-rich, monoclinic, epidote-supergroup minerals ferriakasakaite-(La) and ferriandrosite-(La), found in tephroite Ô calcite veinlets cutting the stratiform ferromanganese deposit from the Shobu area, Ise City, Mie Prefecture, Japan, were studied using electron microprobe analysis and single-crystal X-ray diffraction methods. Ferriakasakaite-(La), ideally A1 Ca A2 La M1 Fe 3+M2 Al M3 Mn 2+ (SiO 4 )(Si 2 O 7 )O(OH) (Z = 2, space group P2 1 /m), has a new combination of dominant cations at A1(Ca) and M3(Mn 2+ ), which are the key sites to determine a root name for epidote-supergroup minerals. The unit-cell parameters are a = 8.8733 (2), b = 5.7415(1), c = 10.0805(3) Å , b = 113.845(2)º and V = 469.73(2) Å 3 . According to the structural refinement (R 1 = 3.13%), the determined structural formula is A1 (Ca 0.54 Mn 2+ 0.46 ) A 2 [(La 0.48 Ce 0.20 Pr 0.07 Nd 0.18 Gd 0.02 ) S 0.95 Ca 0.05 ] M 1 (Fe 3+ 0.42 V 3+ 0.34 Al 0.18 Ti 4+ 0.06 ) M 2 (Al 0.96 Fe 3+ 0.04 ) M 3 ( M n 2 + 0 . 5 0 F e 2 + 0 . 4 3 M g 0 . 0 7 ) ( S i O 4 ) ( S i 2 O 7 ) O ( O H ) . F e r r i a n d r o s i t e -( L a ) , i d e a l l y A1 Mn 2+A2 La M1 Fe 3+M2 Al M3 Mn 2+ (SiO 4 )(Si 2 O 7 )O(OH) (Z = 2, space group P2 1 /m), is the M1 Fe 3+ analogue of androsite. The unit-cell parameters are a = 8.8779(1), b = 5.73995(1), c = 10.0875(2) Å , b = 113.899(1)º and V = 469.97(2) Å 3 , and the structural formula is A1 (Mn 2+ 0.56 Ca 0.44 ) A2 [(La 0.49 Ce 0.20 Pr 0.08 Nd 0.19 Gd 0.02 ) S0.97 Ca 0.03 ] M1 (Fe 3+ 0.40 V 3+ 0.28 Al 0.20 Fe 2+ 0.05 Ti 4+ 0.07 ) M2 (Al 0.97 Fe 3+ 0.03 ) M3 (Mn 2+ 0.50 Fe 2+ 0.40 Mg 0.10 )(SiO 4 )(Si 2 O 7 )O(OH) (R 1 = 2.93%).The two new minerals, which are compositionally very similar overall, are distinguished by occupancy of A1, Ca vs. Mn 2+ . The structural properties of these minerals depend not only on the REE content at A2, but also on the Mn content at A1.

Manganiakasakaite-(La) and Ferriakasakaite-(Ce), Two New Epidote Supergroup Minerals from Piedmont, Italy

“…The statistical tests on the distribution of |E| values and the systematic absences confirmed the space group symmetry P2 1 /m. The crystal structures of both minerals were refined using Shelxl-2018 [14] starting from the atomic coordinates of ferriakasakaite-(La) given by Nagashima et al [2]. The position of the H atom was located through difference-Fourier syntheses.…”

“…Manganiakasakaite-(La) and ferriakasakaite-(Ce) are characterized by the occurrence of REE 3+ at A (2) and Mn 2+ at M(3); a trivalent transition metal (Mn 3+ and Fe 3+ , respectively) is dominant at M (1).…”

“…This shift is associated with a reduction of the Si(1)-O(9)-Si(2) angle, related not only to the site occupancy at A(1) but also to the mean bond length at M(3) [10]. In manganiakasakaite-(La), O(9) is at 3.14 and 3.27 Å from A(1), and the Si(1)-O(9)-Si(2) angle is 140.88(19)°; in ferriakasakaite-(Ce), the same values [20]; solid downward triangle = REE-bearing piemontite [21]; open diamond = ferriakasakaite-(La) [22]; open square = REE-bearing piemontite [19]; crossed open square = (REE,Pb)-rich piemontite [23]; solid square = vanadoallanite-(La) [24]; open circle = Mn 2+ -rich piemontite [25]; crossed open circle = ferriakasakaite-(La) [2]; open downward triangle = ferriandrosite-(La) [2]; solid diamond = manganiandrosite-(La) [19] and manganiandrosite-(Ce) [10]; solid upward triangle = vanadoandrosite-(Ce) [10]. Blue and purple diamonds refer to ferriakasakaite-(Ce) and manganiakasakaite-(La), respectively (this study).…”

“…Then, an adjectival prefix is appended to the root-name for the dominant cation at the M(1) (other than Al), and a Levinson suffix [3] is appended to the root-name for the dominant REE at the A(2) site. The names of the two new minerals are in keeping with the above guidelines, as they represent chemical variants of the mineral ferriakasakaite-(La), which was first described from Japan [2]. Both manganiakasakaite-(La) and ferriakasakaite-(Ce) were found in the Mn ore deposit of Monte Maniglia, Bellino, Varaita Valley, Cuneo Province, Piedmont, Italy.…”

“…According to the general guidelines for the nomenclature of epidotes [1], each distinct combination of dominant cations at the A(1) and M(3) sites deserves a proper root-name. In particular, the root-name "akasakaite" (after Masahide Akasaka, professor of mineralogy at the Shimane University) corresponds to the pair A(1) = Ca and M(3) = Mn 2+ [2]. Then, an adjectival prefix is appended to the root-name for the dominant cation at the M(1) (other than Al), and a Levinson suffix [3] is appended to the root-name for the dominant REE at the A(2) site.…”