Junitoite
| Junitoite | |
|---|---|
Vitreous to pearly junitoite crystals to 4 mm from the Christmas Mine in Gila County, Arizona
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| General | |
| Category | Sorosilicate |
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Formula (repeating unit) |
CaZn2Si2O7·H2O |
| Strunz classification | 9.BD.15 |
| Dana classification | 56.2.1.1 |
| Crystal system | Orthorhombic |
| Crystal class | Pyramidal (mm2) H-M group: (mm2) |
| Space group | Ama2 |
| Unit cell | a = 12.510(7) b = 6.318(3) c = 8.561(6) [Å]; Z = 4 |
| Identification | |
| Color | Colorless, milk-white, or colored due to alteration |
| Cleavage | Good on {100}; poor on {010} and {011} |
| Fracture | Micaceous |
| Tenacity | Brittle to semi-sectile due to alteration |
| Mohs scale hardness | 4.5 |
| Luster | Adamantine, Vitreous, Sub-Vitreous |
| Streak | Colorless |
| Diaphaneity | Transparent to translucent |
| Optical properties | Biaxial (+) |
| Refractive index | nα = 1.656 nβ = 1.664 nγ = 1.672 |
| Birefringence | δ = 0.016 |
| 2V angle | Measured: 86°, Calculated: 88° |
| References | |
Junitoite is a mineral with formula CaZn2Si2O7·H2O. It was discovered at the Christmas mine in Christmas, Arizona, and described in 1976. The mineral is named for mineral chemist Jun Ito (1926–1978).
Junitoite is transparent to translucent and is colorless, milk-white, or colored due to alteration. Crystals grow up to 5 millimetres (0.20 in) and have high quality faces.
Junitoite occurs in fractures through pods of sphalerite. It formed by retrograde metamorphism and oxidation of tactite, also resulting in kinoite. The mineral is known from New Jersey and the type locality in Arizona. Junitoite occurs in association with apophyllite, calcite, kinoite, smectite, and xonotlite.
In 1968, Jun Ito published the results of synthesis of various lead calcium zinc silicates. The formula of one phase, designated X3, was identified as probably CaZnSi2O6·H2O. When he described junitoite, Sidney Williams identified the mineral's formula as CaZn2Si2O7·H2O, based on communications with Ito.
The mineral's crystal structure was first determined in 1985 and refined in 2012. The mineral crystallizes in the orthorhombic crystal system. The structure is formed by chains of corner-sharing ZnO4 tetrahedra linked together by Si2O7 tetrahedral pairs. Calcium ions occupy vacancies and coordinate to five oxygen atoms and one water molecule.
The first known specimen of junitoite was collected from the Christmas mine at Christmas, Arizona, and entered the collection of Joe Ana Ruiz. Geologist Robert A. Jenkins noticed the mineral in kinoite specimens, submitting Ruiz's sample to Sidney A. Williams for study. Further samples came from the collections of Ruiz and Raymond Diaz.
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