Minerals Review Ruby Deposits: a review and Geological Classification Gaston Giuliani


Figure 8. Crystalline forms of the 32/m class of the rhombohedral system, after [38]. (A



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ruby deposits[01-22]
Figure 8. Crystalline forms of the 32/m class of the rhombohedral system, after [38]. (A) positive 
rhombohedron; (B) negative rhombohedron; (C) hexagonal dipyramid; (D) pinacoid; (E) first-order 
hexagonal prism; (F) second-order hexagonal prism; (G) dihexagonal prism; and (H) ditrigonal 
scalenohedron. 
Rubies from Mong Hsu in Myanmar show a number of different habits (Figure 9) [30,45] and are 
bounded by pinacoidal {0001} faces and hexagonal dipyramidal faces {ℎℎ2ℎ𝑙}, sometimes associated with 
small rhombohedral {1011} faces. Second-order prism {1020} faces are also observed in some rubies. The 
smaller dipyramidal faces are {2243}, whereas the larger dipyramidal ones are often reported as {4481} 
or {14 14 28 3}, or less commonly {2241} or {1121}. The {14 14 28 3} indices are too high for smooth faces
and it could be possible that they consist of alternating microsteps between {1120} and {0001} faces [46,47]. 
Rubies from Mogok are generally tabular with predominant pinacoids and rhombohedral {1011} and 
dipyramidal {1121} faces. Other habits (Figure 9) have been reported for marble-hosted rubies from 
Morogoro in Tanzania as flattened to tabular pseudo-cubes, pseudocubes according to the relative size of 
the six rhombohedral faces and six additional prism faces {1021} with a lath-like form [48], and Jegdalek 
in Afghanistan [5]. Rubies in alkali basalt from Thailand and Cambodia are tabular and have combinations 
of rhombohedral {1011} and pinacoid {0001} faces (Figure 9). 
Figure 9. Main habits of ruby from different marble-hosted deposits: Mong Hsu and Mogok in 
Myanmar, Morogoro in Tanzania, and Jegdalek in Afghanistan. The rubies from the Pailin deposit 
(Cambodia) are from alkali-basalt placer deposits. From [5,30,45,48]. 
Figure 8.
Crystalline forms of the 32
/m class of the rhombohedral system, after [
38
]. (A) positive rhombohedron;
(B) negative rhombohedron; (C) hexagonal dipyramid; (D) pinacoid; (E) first-order hexagonal prism;
(F) second-order hexagonal prism; (G) dihexagonal prism; and (H) ditrigonal scalenohedron.
Rubies from Mong Hsu in Myanmar show a number of di
fferent habits (Figure
9
) [
30
,
45
] and are
bounded by pinacoidal {0001} faces and hexagonal dipyramidal faces {hh2hl}, sometimes associated
with small rhombohedral {1011} faces. Second-order prism {1020} faces are also observed in some rubies.
The smaller dipyramidal faces are {2243}, whereas the larger dipyramidal ones are often reported as
{4481} or {14 14 28 3}, or less commonly {2241} or {1121}. The {14 14 28 3} indices are too high for smooth
faces, and it could be possible that they consist of alternating microsteps between {1120} and {0001}
faces [
46
,
47
]. Rubies from Mogok are generally tabular with predominant pinacoids and rhombohedral
{1011} and dipyramidal {1121} faces. Other habits (Figure
9
) have been reported for marble-hosted
rubies from Morogoro in Tanzania as flattened to tabular pseudo-cubes, pseudocubes according to
the relative size of the six rhombohedral faces and six additional prism faces {1021} with a lath-like
form [
48
], and Jegdalek in Afghanistan [
5
]. Rubies in alkali basalt from Thailand and Cambodia are
tabular and have combinations of rhombohedral {1011} and pinacoid {0001} faces (Figure
9
).
Euhedral crystals of ruby can exhibit several faces (Figure 8) that correspond to the following 
crystalline forms [38]: pinacoid {0001}, first-order hexagonal prism {1010}, second-order hexagonal prism 
{1120}, hexagonal dipyramid {hh2hl}, rhombohedron {h0ℎ𝑙}, and ditrigonal scalenohedron {hkil}. 

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