Epidote-(Sr), CaSrAl
2Fe
3+(Si
2O
7)(SiO
4)(OH), the Sr-analog of epidote, was found in the Nagakawara and Hohnomori deposits at the Ananai mine, Kochi Prefecture, Japan. It occurs in the form of prismatic crystals up to 1 cm in length in the tinzenite veins or the fine crystal aggregates in piemontite breccia. Epidote-(Sr) is optically biaxial negative,
α = 1.737(2),
β = 1.780 (2),
γ = 1.792 (2), and 2
Vcalc = 62° and has perfect cleavage parallel to {001}. It exhibits pleochroism—
X: pale greenish yellow, and
Y and
Z: pale reddish brown to brownish pink. Its calculated density is 3.74 g/cm
3, and it has a Mohs' hardness of 6.5. The representative empirical formula of epidote-(Sr) from the Nagakawara deposit is (Ca
1.10Sr
0.90)
Σ2.00 (Al
1.92Fe
3+0.87Mn
3+0.20)
Σ2.99Si
3.01O
12(OH) on the basis of OH = 1 and O = 12 per formula unit. The mineral is monoclinic with a space group of
P2
1/
m,
a = 8.928 (5),
b = 5.652 (1),
c = 10.244 (5) Å,
β = 114.46 (4)°,
V = 470.5 (3) Å
3, and Z = 2. The strongest seven lines in the X-ray powder diffraction pattern [
d in Å (
I/I0) (
hkl)] were 2.92 (100) (11-3), 2.58 (49) (202), 3.50 (42) (21-1), 2.61 (42) (31-1), 2.72 (41) (013), 2.83 (32) (020), and 3.26 (23) (201). Epidote-(Sr) from the Nagakawara deposit may have been formed from the residual hydrothermal fluid after the crystallization of tinzenite.
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