Magnesio-arfvedsonite from Jade Mine Tract, Myanmar: mineral description and crystal chemistry

Abstract

Magnesio-arfvedsonite, the C Fe 3+ -dominant analogue of eckermannite, has been found in a sample of ''szechenyite'' in the mineral collection of the American Museum of Natural History (AMNH H35024). It comes from the northern part of the Jade Mine Tract near Hpakan, Kachin State, Myanmar. Associated minerals are kosmochlor-jadeite solid-solution pyroxene and clinochlore. The ideal formula of magnesio-arfvedsonite is A Na B Na 2 C (Mg 4 Fe 3+ ) T Si 8 O 22 W (OH) 2 , and the empirical formula derived from electron microprobe analysis and single-crystal structure refinement for the sample of this work is A (Na 0.96 K 0.04 ) S=1.00 B (Na 1.57 Ca 0.40 Fe 2+ 0.02 Mn 0.01 ) S=2.00 C (Mg 4.26 Fe 2+ 0.19 Fe 3+ 0.41 Al 0.11 Ti 4+ 0.03 ) S=5.00 T (Si 7.99 Al 0.01 ) S=8.00 O 22 W [F 0.02 (OH) 1.98 ] S=2.00 . The unit-cell dimensions are a = 9.867(1), b = 17.928(2), c = 5.284(1) Å , b = 103.80(2)º, V = 907.7 (2) Å 3 , Z = 2. Magnesio-arfvedsonite is biaxial (À), with a = 1.624, b = 1.636, g = 1.637, all Ô 0.002 and 2V obs = 36(1) o , 2V calc = 32 o . The ten strongest reflections in the X-ray powder pattern [d values (in Å ), I, (hkl)] are:

Khan River and Bear Lake: Two Natural Titanite Reference Materials for High‐Spatial Resolution U‐Pb Microanalysis

“…This region is located at the south-eastern edge of the amphibolite-facies Glamorgan Gneiss Complex, in the strongly deformed Central Metasedimentary Belt of the Grenville Province (Hewitt 1956). It is known for the occurrence of different types of coarse-grained world-class mineral specimens, such as biotite, apatite, amphibole, titanite, feldspar and uranothorite (Satterly 1943, Armstrong and Gittins 1968, Oberti et al 2019. The titanite at this locality occurs in 1-2 m wide, E-W trending calcite veins or dykes ('vein-dykes', Heinrich 1966); similar calcite vein-dykes are common throughout the Central Metasedimentary Belt Boundary Zone.…”

“…The origin of the calcite vein-dykes is contentious; they have been interpreted to represent primary carbonatitic melts (Heinrich 1966), metamorphosed and remobilized carbonatites (Moecher et al 1997), or to reflect melting of carbonate rocks (Oberti et al 2019). Moecher et al (1997) obtained titanite U-Pb ID-TIMS ages in the range 1085-1035 Ma from different skarns.…”

Mangani-eckermannite, NaNa2(Mg4Mn3+)Si8O22(OH)2, a new amphibole from Tanohata Mine, Iwate Prefecture, Japan

“…At lower hierarchical levels, it belongs to the sodium amphiboles subgroup within the group of W (OH,F,Cl)-dominant amphiboles. It is the Mn 3+ -dominant analogue of eckermannite A Na B Na 2 C (Mg 4 Al) T Si 8 O 22 W (OH) 2 (Oberti et al , 2015b) and magnesio-arfvedsonite A Na B Na 2 C (Mg 4 Fe 3+ ) T Si 8 O 22 W (OH) 2 (Oberti et al , 2015a). For the comparison of the three species see Table 8.…”

Locality determination of inky black omphacite jades from Myanmar and Guatemala by nondestructive analysis

“…The six amphibole species are magnesiokatophorite, nyböite, eckermannite, glaucophane, richterite, and winchite. [33,[45][46][47][48][49][50][51] Notably, taramite is a common accessory mineral in Guatemalan feicui but has not been found in Myanmar feicui, making it very important in origin determination. [33,35,37,[45][46][47][48]52,53] 3.2 | Omphacite composition differences between Myanmar and Guatemalan jade…”