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Garnet Crystal System: cubic. Almandine garnet crystal, cubic mineral, exclusive garnet crystals, garnets information and data
Red - violetish: Hardness Density Ref.Index
Pyrope    Mg3Al2Si3O12 7,25 3,58 g / cm3 1,714
Almandine Fe3Al2Si3O12 7,50 4,32 1,830
Rhodolite Mg,Fe3Al2SiO12 7,25 3,78 - 3,90 1,74 -1,78
Orange - yellow-brown :
Spessartite Mn3Al2Si3O12 7,25 4,20 - 4,25 1,78 - 1,81
Malaya (Mg,Fe,Mn,Ca)3Al2(SiO4)3 7,25 3,74 - 4,00 1,78
Hessonite   Ca3Al2(SiO4)3 7,25 3,58 - 3,65 1,73 - 1,74
Green :
Tsavolite     Ca3Al2(SiO4)3 7,25 3,60 - 3,68 1,73 - 1,74
Uvarovite     Ca3Cr2Si3O12 7,50 3,85 1,87
Dementoïde Ca3F2SiO12 6,5 - 7 3,82 - 3,85 1,89


In a perfect crystal, when a face appears in the crystal in the process of growth, all the faces appear with the same
If one of the symmetrical faces is less developed on a crystalline sample, or exceptionally does not appear, that
comes from the accidental actions of the external environment which opposed its growth.
Temperature, pressure, nature of the mineral solution, speed of the crystalline growth and the direction of the
movement of solution etc... represent the external influences on the crystalline shapes.
The frequency of the faces of the crystals is related to the reticular density, the fast growth of some faces
influences the crystalline shape definitively.
Garnet thus crystallizes under the cubic system, which crystals are characterized by the presence of three
quaternary axes A4 joining the centers of the faces, four ternary axes A3 joining the opposed tops, six binary
axes A2 joining the mediums of the edges.
· One of the causes modifying the initial shape of crystals is truncation.
Truncation on corners.
Cube Dodecahedron
Truncation cuts two different lengths on adjacent corners.
Cube Tetrahexahedron
Truncation cutting three equal lengths out of the three adjacent corners.
Cube Octahedron
Truncation cuts two equal lengths out of two corners and a larger length on the third.
Trisoctahedron Octahedron
Truncation on the segment crosses, two equal lengths out of two corners, a smaller length on the third.
Cube Trapesohedron
Octahedron Trapesohedron
Dodecahedron Trapesohedron
Hexoctahedron Dodecahedron
Almandine in matrix Pyrope-Almandine Almandine in matrix
Almandine in matrix Almandine in matrix Rhodolite (Ambohitompoina)
There is also a law according to which certain crystals do not present modifications that on half of corners, or of the
similar angles.
Here is a truncation on a top cutting three different lengths on corners, and which repeats only three times around
the ternary axis.
Cube and diplohedron Diplohedron Right Gyrohedron  Left Gyrohedron
The diplohedron is made of twenty-four irregular quadrilaterals. The class plagiohedron which faces (HKL) are 
arranged in the spiral order. 
In other cases, twelve irregular pentagons are formed by a truncation on one sharp angle, on both adjacent angles, the
unequal lengths, it is the pentagonal dodecahedron.  
Positive  Negative
Almandine in matrix Tsavolite (Madagascar) Spessartite in pegmatite
The regular tetrahedron consisted four equilateral triangles forming between them an angle of 70° 31.
Positiv tetrahedron  Négativ tetrahedron Octahedron
 Positiv tetrahedron Cube
The tetrahedron or triakistetrahedron consisted twelve faces which are isosceles triangles, and the hexatetrahedron 
with its twenty four triangular faces. 
Triakistetrahedron Hexakistetrahedron
The trapezoidal dodecahedron consisted twelve quadrilaterals deltoid and the tetrahedral pentagonal dodecahedron
are formed by a truncation appearing on each top and cutting three different lengths on angle.
  right left
Deltoid dodecahedron Pentagonal tetraedrical dodecahedron . Almandine in matrix
Oval Spessartite garnet, orange gemstone, exclusive spessarites gemstones, garnets information Oval Malaya garnet, orange cinnamon gemstone, exclusive Malaya garnets gemstones, garnets information
Spessartite (Ambohimarangitra) Malaya  (Andoharano) Malaya  (Madagascar)
Oval Rhodolite garnet, purple red pink gemstone, exclusive rhodolites gemstones, garnets information Oval Hessonite garnet, orange cinnamon gemstone, exclusive hessonites gemstones, garnets information Oval Malaya garnet, orange cinnamon gemstone, exclusive Malaya garnets gemstones, garnets information
Rhodolite  (Ankilytokana) Hessonite  Malaya  (Madagascar)
In Madagascar, one finds rhodolite in a gneiss rich in biotite, in which (almandite-pyrope) is presented in the form of
small grains, or in the state of large porphyroblasts, generally deprived of geometrical contours, plagioclase
(oligoclase with andesine) is the feldspar dominating and sometimes exclusive. These gneisses contain sometimes
pegmatic beds very rich in crystals.
One very finds also garnetiferous gneisses containing little biotite, hardly directed.
Kinzigites. The gneisses which have been just enumerated have a very clear schisteous structure, which had with the
biotite abundance. A rather frequent type is approximately blocks and presents a compact aspect, thanks to the
prevalence of large garnets without geometrical form, associated quartz and granoblastic feldspar, biotite is not
very abundant. The structure points out that of corneal micaceous of contact of the granite. This gneiss can be
compared with the kinzigite of the Black Forest. 
Leptynites with amphibolo-pyroxenite intercalation rich in garnets of a pale pink (almandite-pyrope), with often
rutile and graphite abound in certain areas of Madagascar. The feldspar is orthoclase, associated with
ogigoclase-albite feldspar and sometimes with spindle-shaped microperthite, there exists much of myrmekite.
These rocks are with fine grins, but they very often contain large regularly distributed crystals.
Usually garnet does not have a geometrical form, but it takes clear faces in more quartzose zones.
Leptynites derive from the granites by disappearance of the mica; the garnetiferous mica schists constitute the
opposed pole in which biotite prevails, with progressive disappearance of feldspar. 
  The Besafotra river carry out spessartites
  on several kilometers from their source,
  doubtless a sodolitic pegmatite.
  A walk of 25 kilometers among the mountains
  is necessary to reach this place. 
The tanety "grounds bordering the river," are also
the object of the orange garnet's fever. 
Sifting in river.
Initially, the spessartite appeared in the
Besafotra river, searched out here near to 
its source. 
Ankilytokana, one of the fabulous rhodolite occurrences 
exploited in a leptynite vein on a sixteen meters depth. 
Leptynites are primarily consisted in alkaline feldspars 
and quartz. When these rocks are not ribboned, and 
that is frequent, it is often difficult to decide if a sample, 
not seen in place, belongs to a leptynite or an aplite, it
should be noticed that in Madagascar, these last
contain microcline and not orthoclase. In this area,
one observes graphite spangles in the leptynites.
 Malaya garnet discovered into
 September 1998, in eluvium in
 a broken up leptynite.
 The modest depth of the deposit did
 not require any significant work to
 extract it.
This stone shows an exceptional capacity to restore 
the light, thanks in particular to its high refractive index, 
especially under not very enlightened condition.
Malaya Garnet Discovery
Cutting Styles¦Characteristics¦ Crystalline Systems ¦ Madagascar Sapphire ¦ Corundum data
¦ Malaya Garnet ¦ Rhodolite Garnet ¦ Spessartite Garnet ¦ Hessonite Garnet ¦
Your guide to GGGems
© All of the pictures on this website have been shot by Alain Darbellay
     Text written by Alain Darbellay.
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