Exsolution lamellae and optic orientation of clinoamphiboles

Howard W. Jaffe*, Peter Robinson, Cornelis Klein

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

1 Citation (Scopus)


Exsolution lamellae are abundant in coexisting hornblende and cummingtonite, and in hornblende coexisting with anthophyllite in Ordovician volcanics metamorphosed in the kyanite and sillimanite zones in central Massachusetts and adjacent New Hampshire. The lamellae have the same orientation relative to the internal structure as the (100) and (001) exsolution lamellae in clinopyroxenes, but are indexed (100) and (101) with the C2/m space group commonly chosen for amphiboles. Specimens from the kyanite zone contain very thin (100) and (101) lamellae. In the sillimanite zone, both (100) and (101) lamellae are thicker and more abundant in iron-rich specimens than they are in magnesian specimens, as might be expected by analogy with pyroxenes from layered mafic intrusions. The (101 lamellae allow correct determination of the relations between the optic vibration directions and the crystallographic axes for two alternatively selected space group C2/m and I2/m. This evidence shows that there has been much confusion concerning these relations.

Original languageEnglish
Pages (from-to)776-778
Number of pages3
Issue number3829
Publication statusPublished - 1968
Externally publishedYes


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