THE X-RAY STUDY AND THERMAL ANALYSIS OF AMPHIBOLES

Abstract

The results of X-ray and thermal analysis of amphiboles can provide insights into their commercial significance and the nature of discordant K-Ar age determinations. Conclusions (1) The unit cell parameters of amphiboles undergo a marked change in a temperature range from 500 to 900°C; (2) unit cell volumes V and lattice parameters a, b, and c of hornblende, arfvedsonite, and pargasite decrease from 500 to 900°C, while the unit cell volume of the riebeckite unit cell passes a minimum at 600°C; (3) angle β for all the studied amphiboles remains constant in a range of 25-900°C, indicating that amphiboles can retain their structure in a wide temperature range; and (4) owing to the thermal stability of the crystal lattice, amphiboles retain radiogenic Ar almost entirely and, thus, can be dated with the K-Ar method.