16.20: Axinite
- Page ID
- 4356
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\(\newcommand{\avec}{\mathbf a}\) \(\newcommand{\bvec}{\mathbf b}\) \(\newcommand{\cvec}{\mathbf c}\) \(\newcommand{\dvec}{\mathbf d}\) \(\newcommand{\dtil}{\widetilde{\mathbf d}}\) \(\newcommand{\evec}{\mathbf e}\) \(\newcommand{\fvec}{\mathbf f}\) \(\newcommand{\nvec}{\mathbf n}\) \(\newcommand{\pvec}{\mathbf p}\) \(\newcommand{\qvec}{\mathbf q}\) \(\newcommand{\svec}{\mathbf s}\) \(\newcommand{\tvec}{\mathbf t}\) \(\newcommand{\uvec}{\mathbf u}\) \(\newcommand{\vvec}{\mathbf v}\) \(\newcommand{\wvec}{\mathbf w}\) \(\newcommand{\xvec}{\mathbf x}\) \(\newcommand{\yvec}{\mathbf y}\) \(\newcommand{\zvec}{\mathbf z}\) \(\newcommand{\rvec}{\mathbf r}\) \(\newcommand{\mvec}{\mathbf m}\) \(\newcommand{\zerovec}{\mathbf 0}\) \(\newcommand{\onevec}{\mathbf 1}\) \(\newcommand{\real}{\mathbb R}\) \(\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}\) \(\newcommand{\laspan}[1]{\text{Span}\{#1\}}\) \(\newcommand{\bcal}{\cal B}\) \(\newcommand{\ccal}{\cal C}\) \(\newcommand{\scal}{\cal S}\) \(\newcommand{\wcal}{\cal W}\) \(\newcommand{\ecal}{\cal E}\) \(\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}\) \(\newcommand{\gray}[1]{\color{gray}{#1}}\) \(\newcommand{\lgray}[1]{\color{lightgray}{#1}}\) \(\newcommand{\rank}{\operatorname{rank}}\) \(\newcommand{\row}{\text{Row}}\) \(\newcommand{\col}{\text{Col}}\) \(\renewcommand{\row}{\text{Row}}\) \(\newcommand{\nul}{\text{Nul}}\) \(\newcommand{\var}{\text{Var}}\) \(\newcommand{\corr}{\text{corr}}\) \(\newcommand{\len}[1]{\left|#1\right|}\) \(\newcommand{\bbar}{\overline{\bvec}}\) \(\newcommand{\bhat}{\widehat{\bvec}}\) \(\newcommand{\bperp}{\bvec^\perp}\) \(\newcommand{\xhat}{\widehat{\xvec}}\) \(\newcommand{\vhat}{\widehat{\vvec}}\) \(\newcommand{\uhat}{\widehat{\uvec}}\) \(\newcommand{\what}{\widehat{\wvec}}\) \(\newcommand{\Sighat}{\widehat{\Sigma}}\) \(\newcommand{\lt}{<}\) \(\newcommand{\gt}{>}\) \(\newcommand{\amp}{&}\) \(\definecolor{fillinmathshade}{gray}{0.9}\)| Axinite | |
|---|---|
| Chemical composition | Complex borosilicate |
| Crystal system | Triclinic |
| Habit | Axe shaped. |
| Cleavage | Perfect {100} |
| Fracture | Uneven to conchoidal, brittle |
| Hardness | 6.5 - 7 |
| Optic nature | Biaxial - (or +) |
| Refractive index | 1.674 - 1.706 |
| Birefringence | 0.010 - 0.012 |
| Dispersion | Low, 0.018 - 0.020 |
| Specific gravity | 3.27-3.29 |
| Lustre | Bright vitreous |
| Pleochroism | Moderate to Strong |
Figure \(\PageIndex{1}\): A pinkish/greenish brown axinite.
Photo courtesy of Chaman Golecha, Gem Testing Laboratory, Jaipur.
Chemical composition
Ca3Al2BSi4O15(OH). Much variation in composition due to replacement of Ca by Fe, Mg, Mn. Therefore the composition may be written as (Ca, Mn, Fe, Mg)3Al2BSi4O15(OH)
- +Mg - magnesioaxinite
- If Fe more than Mn - Ferroaxinite
- If Mn more than Fe - Manganaxinite
- If Mn more than Fe and Ca less than 1.5 - tinzenite
Crystallography
Triclinic.
Habit: broad and acute edged usually (axe shaped); varied habit; Also massive, lamellar, granular, curved. Generally in clusters, also tabular.
Diagnostics
Color
Clove Brown, rarely honey yellow or plum blue. Also pearly gray, greenish yellow; violet-brown; colorless-yellowish(Mn); pale violet/reddish (Mn), blue (Mg).
Diaphaneity
Transparent to semi transparent.
Hardness
7-6.5 (directional)
Specific gravity
3.27-3.29 [Ferroaxinite:3.17-3.31; Magnesioaxinite:3.18; range 3.26-3.36]
Refractometer
Optic Character: anisotropic; Biaxial Negative (If high in Mg may turn +ve).
R.I.: nα = 1.674-1.693, nβ = 1.680-1.701 and nγ = 1.684-1.706.
Generally R.I.:1.67 to 1.68
Maximum birefringence: 0.010 - 0.012
Spectrum
Strong bands at 512, 494, 466 and sometimes 415nm; strong lines at 523, 444.
Luminescence
UV fluorescence: May show red-orange under SWUV
Pleochroism
Strong depending on body colour and source. Generally olive green/violet blue and cinnamon brown.
Simulants
- Andalusite: Lower S.G., spectrum, R.I. etc
- Barite: Higher heft, lower hardness
- Smoky Quartz: Lower Heft (floats 2.88), bulls-eye optic figure, R.I. etc
- Sphene: Doubling, dispersion, spectrum
Occurrence
Geological occurrence:
Occurs in cavities of granite or diabase; contact zones
Geographical locations:
Good crystals from St. Cristophe, France; various American localities; Bahia, Brazil; Cornwall, England; Mexico; Also in California; Sri Lanka; Nevada (masses); New Jersey; Germany; Norway; Finland; USSR; Japan; Tasmania; Switzerland (Tinzenite); Tanzania (Magnesoaxinite); Sri Lanka (ferro axinite-cinnamon brown)