Rankin and Wright — Ternary System CaO-Al 2 0,-Si0. 2 . 75 



s 



B 



Plane of optic axes 

 parallel to elongation. 



Intricate polysynthetic 

 twinning is character- 

 istic of this form. 



Birefringence very weak. 



Birefringence very weak. 

 Twinning lamellae 

 not uncommon. 



Refractive indices 

 slightly lower than in 

 natural mineral. 



Occasionally gray inter- 

 ference colors appear 

 as result of strain. 



Stable form. 



Plane of optic axes 

 parallel with fiber 

 elongation. 



* 6 

 .2 £ 



bO * 



g«2 

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Indications of small 2 E 

 noted in some sections. 



Axial dispersion strong 

 2V r >2V v . Plane of 

 optic axes parallel with 

 fiber elongation. 



Polysynthetic twinning 

 characteristic. 



Crystallizes readily. 



Usually in fine fibrous 

 aggregates. Plane of 

 optic axes parallel to 

 fiber elongation. 



Optic 

 axial 

 angle 



large 



large 



small or 

 uniaxial(?) 





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 orienta- 

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c:a' = 18° 



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Crystal 

 habit 



irreg. grains 



prisms 



irregular 



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 grains 

 fibers 

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 grains 

 fibers 

 prisms 





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Crystal 

 system 



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or monoclinic 



monoclinic or 



tri clinic 



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