Amethyst with Hollandite
78.71 ct
Cushion Cut
30.10 x 20.20 x 15.80 mm
Origin Brejinho,
Bahia,
Brazil.
Date Found 2020
max888
ホーランダイト入りアメジスト

At first the visual test appeared to be hollandite. This material belongs to a group of similar members  ,but is different from the well  known “star hollandite” from Madagascar. Star hollandite is an intergrowth of needles crossing each other, in this case instead the needles departing from a single point.

Research and tests performed at the Università La Sapienza in Rome:
1- A scanning electron microscope (SEM) Carl Zeiss SEM EVO 50 + energy dispersive spectrometer EDS.
2-Microprobe EMP + wavelength dispersive spectroscopy (WDS).

Empirical formula:

a (Ba0,981 Pb0,256 Na0,097 K0,013)Σ1,348m ( Mn4+4,916 Mn3+2,504 Ti0,339 Si0,160 Fe3+0,046 Al0,035)Σ8,000O16

ideal formula:Ba(Mn4+6Mn3+2)O16

Ferrihollandite  - empirical formula:

(Ba0,793 Sr0,222 Na0,024 K0,009)Σ= 1,048 (Mn4+ 5,624 Ti0,318 Fe3+1,016 Mn3+ 0.910 Al0,129 Zn 0,003)Σ=8.000 O16

ideal formula:Ba(Mn4+6Mn3+2)O16

Ferricoronadite - empirical formula:

( Ba0,32 Pb1,03)Σ= 1,350 (Mn4+ 4,85 Ti0,49 Fe3+ 1,35 Mn3+ 1.18 Al0,09 Zn0,04) Σ=8.000 O16

ideal formula: Ba(Mn4+6Mn3+2)O16