Biaxiality in relation to visible twinning in experimentally deformed calcite

✍ Scribed by Francis J. Turner

• Publisher: Springer
• Year: 1975
• Tongue: English
• Weight: 1013 KB
• Volume: 53
• Category: Article
• ISSN: 0010-7999
• DOI: 10.1007/bf00382442

✦ Synopsis

Moderate to strong biaxiality (2V=10~ ~ in experimentally deformed calcite (in single crystals and in marble) is attributed to overlap between one or two thin {01i2} twin lamellae and the enclosing host. A perfectly centered conoscopic figure (section normal to [0001]) is perceptibly asymmetric about the trace of the optic axial plane. This asymmetry is pronouned in thick sections (>0.04 mm) and completely distrupts the biaxial configuration of the figure if the overlapping lamella exceeds about 0.0025 mm in thickness. In sections somewhat oblique to [0001] and cut at 20 ~ or less to the plane of twinning the conoscopic figure may appear to be perfectly biaxial-expecially in thin sections (~0.02 ram) enclosing thin (~0.001 mm) but still visible twins.

Similar values of 2V recorded for natural calcite likewise are attributed to twinning on a visible scale.