General
Formula: [Ca2][Al2Fe3+](Si2O7)(SiO4)O(OH)
Crystal system: Monoclinic
Distinguishing features
N // (PPL)
Color: yellow or greenish-yellow
Pleochrosim: colourless to yellow
Relief: strong
Cleavage: perfect after {001}
N + (XPL)
Isotropy/Anisotropy: anisotropic
Interference color: II-III (very bright or ‘fluorescent’)
Extinction angle: parallel / 0° to length of elongate crystals and inclined extinction relative to its {001} cleavage
Twins: –
Uniaxial/biaxial: Biaxial (-)
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