16.8.3: Grossular
- Page ID
- 4134
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\(\newcommand{\avec}{\mathbf a}\) \(\newcommand{\bvec}{\mathbf b}\) \(\newcommand{\cvec}{\mathbf c}\) \(\newcommand{\dvec}{\mathbf d}\) \(\newcommand{\dtil}{\widetilde{\mathbf d}}\) \(\newcommand{\evec}{\mathbf e}\) \(\newcommand{\fvec}{\mathbf f}\) \(\newcommand{\nvec}{\mathbf n}\) \(\newcommand{\pvec}{\mathbf p}\) \(\newcommand{\qvec}{\mathbf q}\) \(\newcommand{\svec}{\mathbf s}\) \(\newcommand{\tvec}{\mathbf t}\) \(\newcommand{\uvec}{\mathbf u}\) \(\newcommand{\vvec}{\mathbf v}\) \(\newcommand{\wvec}{\mathbf w}\) \(\newcommand{\xvec}{\mathbf x}\) \(\newcommand{\yvec}{\mathbf y}\) \(\newcommand{\zvec}{\mathbf z}\) \(\newcommand{\rvec}{\mathbf r}\) \(\newcommand{\mvec}{\mathbf m}\) \(\newcommand{\zerovec}{\mathbf 0}\) \(\newcommand{\onevec}{\mathbf 1}\) \(\newcommand{\real}{\mathbb R}\) \(\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}\) \(\newcommand{\laspan}[1]{\text{Span}\{#1\}}\) \(\newcommand{\bcal}{\cal B}\) \(\newcommand{\ccal}{\cal C}\) \(\newcommand{\scal}{\cal S}\) \(\newcommand{\wcal}{\cal W}\) \(\newcommand{\ecal}{\cal E}\) \(\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}\) \(\newcommand{\gray}[1]{\color{gray}{#1}}\) \(\newcommand{\lgray}[1]{\color{lightgray}{#1}}\) \(\newcommand{\rank}{\operatorname{rank}}\) \(\newcommand{\row}{\text{Row}}\) \(\newcommand{\col}{\text{Col}}\) \(\renewcommand{\row}{\text{Row}}\) \(\newcommand{\nul}{\text{Nul}}\) \(\newcommand{\var}{\text{Var}}\) \(\newcommand{\corr}{\text{corr}}\) \(\newcommand{\len}[1]{\left|#1\right|}\) \(\newcommand{\bbar}{\overline{\bvec}}\) \(\newcommand{\bhat}{\widehat{\bvec}}\) \(\newcommand{\bperp}{\bvec^\perp}\) \(\newcommand{\xhat}{\widehat{\xvec}}\) \(\newcommand{\vhat}{\widehat{\vvec}}\) \(\newcommand{\uhat}{\widehat{\uvec}}\) \(\newcommand{\what}{\widehat{\wvec}}\) \(\newcommand{\Sighat}{\widehat{\Sigma}}\) \(\newcommand{\lt}{<}\) \(\newcommand{\gt}{>}\) \(\newcommand{\amp}{&}\) \(\definecolor{fillinmathshade}{gray}{0.9}\)| Grossular Garnet | |
|---|---|
| Chemical composition | Ca3Al2(SiO4)3alcium aluminum silicate |
| Crystal system | Cubic |
| Habit | Dodecahedra |
| Cleavage | None |
| Hardness | 7.0-7.5 |
| Optic nature | Isotropic |
| Refractive index | 1.738-1.745 |
| Birefringence | None |
| Specific gravity | 3.60-3.68 |
| Lustre | Vitreous |
Diagnostics
Color
Green, yellowish-green, yellow-orange and pastel.
Inclusions
Hessonite: granular internal structure from numerous crystal inclusions, giving it an oily appearance.
Green grossular: rod-like or needle-like crystals.
Hydrogrossular: granular structure often with irregular black inclusions.
Refractometer
Hessonite and green grossular: 1.73-1.76 (singly refractive)
Hydrogrossular garnet: 1.70-1.73 (singly refractive)
Specific gravity
Grossular garnets sink in all common heavy liquids. Hydrogrossular garnet may sink slowly in methylene iodide.
Hessonite and green grossular garnet: 3.60-3.70
Hydrogrossular garnet: 3.35-3.55
Chelsea Colour Filter
Green stones may appear pinkish to red.
Varieties
Hessonite
Hessonite is the brownish-red to yellowish-orange variety.
Green grossular garnet
Figure \(\PageIndex{1}\): Faceted Mint Garnet
Photo courtesy of Ben Pfeiffer
Green grossular garnet is the bluish-green to yellowish-green variety. Within this group, Merelani Mint garnet is a grossular variety that is found in the Merelani Hills of Tanzania. It has emerged in the last few years with a bright pastel mint green color. Due to its limited availability, it has remained mainly as a collector stone.
Hydrogrossular garnet
Hydrogrossular garnet is the green, pink, grayish-white to bluish variety of grossular.
Chrome grossular
Chrome grossular is a green variety of grossular.
Tsavorite
Tsavorite (or tsavolite) is a grossular that, like the Meralani mint, is green in colour. It is coloured by chromium and/or vanadium. The distinction between a 'regular' green grossular and tsavorite is commonly thought to be a function of saturation and tone. However, according to the Bridges' family (tsavorite was discovered by the late Campbell Bridges), the distinction is chemical. The chromophore for green grossular is iron, as opposed to chromium and/or vanadium.
Mali
Mali garnet is a yellow-green variety of grossular with a slight overlap in the grossular-andradite series.