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Chemical Formula | (Below is the chemical formula for the
common garnets. A more comprehensive list can be found in
"The chemical formula of Garnet") X
2+3
Y 3+2
Si 3 O
12 |
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Composition | This is a list of the composition of members
of the Garnet Group. Minerals intermediary between two or more members do
exist. Pyrope - Magnesium aluminum silicate Almandine - Iron aluminum silicate Spessartine - Manganese aluminum silicate Grossular - Calcium aluminum silicate Andradite - Calcium iron silicate Uvarovite - Calcium chromium silicate |
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Color | Red, brown, black, green, yellow, orange,
pink, white, and colorless. Massive specimens from certain localities are
multicolored white, pink, and/or light green. Garnet occurs in shades of all colors except for blue. Each garnet forms in particular colors, as mentioned: Pyrope - Deep red to nearly black Almandine - Deep red to reddish-brown, sometimes with a violet or brown hue Spessartine - Brown, orange, and pink Grossular - Colorless, white, green, yellow, pink, brown, orange and orange-red Andradite - Red, green, yellow, brown, black; rarely colorless Uvarovite - Emerald-green |
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Streak | Colorless |
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Hardness | 6½ - 7½. Almandine from one locality can be as hard as 8½. |
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Crystal Forms and Aggregates |
(Isometric) Occurs in well-formed, distinct, dodecahedral and trapezohedral crystals. Also occurs in compact crystal groupings, grainy, massive, as rounded crystals, and as groups of small crystals. |
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Transparency | Transparent to opaque |
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Specific Gravity | 3.5 - 4.3 |
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Luster | Vitreous to adamantine |
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Cleavage | None. May exhibit parting. |
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Fracture | Conchoidal to uneven |
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Tenacity | Brittle |
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Other ID Marks | Almandine is paramagnetic, and becomes magnetic upon heating. |
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Other Names | See each individual member |
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Varieties | See each individual member for varieties of that member |
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In Group | Silicates ; Nesosilicates |
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All About | The Garnet group contains closely related, isomorphous minerals that may intergrow or
contain a slight percentage of another element found in a
different garnet member replacing one of its own. The
common garnets can be divided into two classifications: Group 1: Garnets containing aluminum (Al) as their second element Group 2: Garnets containing calcium (Ca) as their first element Some people gives these groups names: Group 1 is called "Pyralspite", as an acronym for the garnets contained in that group: Pyrope, Almandine, and Spessartine. Group 2 is called "Ugrandite", as an acronym for the garnets contained in that group: Uvarovite, Grossular, and Andradite. The members of each group freely intermingle among each other. For example the Magnesium in Pyrope may be partially replaced by some iron from Almandine or by some manganese from Spessartine. However, between the two groups of Garnets, it is much rarer for them to intermingle (such that an element from a garnet from the first group is partially replaced by an element found in a garnet of the second group). The garnets vary only slightly in physical properties, and some of the members may be so similar that they are indistinguishable from one another without x-ray analysis. Garnet as a group is one of the most common minerals. However, some individual members or varieties of individual members are quite rare, and are in high demand by collectors and for their use as gems. Garnets crystallize in the isometric system, but only form in dodecahedral and trapezohedral crystals. Crystals may be quite large and well formed, providing perfect crystal replicas. Aggregates showing fine crystal developments are also very attractive. Garnet is a popular gem. The most famous gem varieties are Pyrope and Almandine. The most valuable garnet gem, however, is the Demantoid variety of Andradite. The definition of Carbuncle is a deep red Garnet cut into a cabochon. In the gem trade, when the term "Garnet" is used, it refers to a garnet of dark red color, and usually to Pyrope or Almandine. |
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Uses | Garnets have many practical uses.
Transparent varieties of cuttable size are faceted for
jewelry, and dark red Garnet is the most popular form.
The harder garnets are used as an abrasive, from which Garnet paper, a popular sandpaper, is made of.
Well formed crystals and interesting aggregates very
popular among mineral collectors. See the gemstone section on garnet |
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Striking Features | Crystal forms and hardness |
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Popularity (1-4) | 1 |
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Prevalence (1-3) | 1 |
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Demand (1-3) | 1 |
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Distinguishing Similar Minerals |
Zircon - Heavier, forms in different
crystals, usually fluoresces (whereas Garnet does not) Ruby - Harder (9) Spinel - Occurs in different crystals than Garnet Tourmaline - Lighter in weight. Careful analyzation can distinguish a different crystal form than Garnet if the Tourmaline occurs in short, rounded crystals |
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Commonly Occurs With |
Mica, Feldspar, Quartz, Calcite, Staurolite, Chlorite, Diopside, Olivine, Hornblende |
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Noteworthy Localities |
Different members occur in different localities. Each individual member has its localities listed under its own exclusive page. Links to each member are on the top of the page. |
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Picture Icon Links |
Sorry. No Images currently available. |
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Picture Links | Sorry. No Images currently available. |
