THE ELASTO-OPTIC EFFECT IN POLYCRYSTALLINE AGGREGATES. Dr.Sc., Ph.D. Alexander Kh. Zilbershtein, Institute of Precambrian Geology & Geochronology, Russia Acad. Sci., St.-Petersburg, Russia
The mutual strain {X} for different elements (parts) of the aggregate may exist, if the temperature Tf and/or the pressure Pf of polycrystalline aggregate's formation are not equal to the temperature T and pressure P under study. This mutual strain induces the elasto-optic effect in these elements. The effect may be designed as induced birefringence dN for transparent materials or double reflection dR for strongly absorbing ones. These optical anomalies may be used for determining of the mutual strain {X} and, in turn, for estimation of the unknown values of the Tf and the Pf. The latter data are artificial and natural expressions for the dN useful for various problems of a growth of crystals, compounds and aggregates. The expressions for the dN and the dR as a function of the Tf and the Pf were obtained. The simple form of the expression for elastoisotropic approximation may be presented as
dN=A(B(Tf-T)+C(P-Pf))
where the A is the proper combination of the elasto-optic constants for the investigated crystal element of the aggregate; the B (and the C) is the difference between the thermal expansion (and compliances) coefficients for the investigated element and the corresponding neighbouring different element. The unknown parameters of aggregates formation (Tf) were obtained for first time, using measured value of the |dN| and experimentally obtained function |dN(T)| as well as known values of the T, the P, the B, the C:, the Pf, for natural quartz-feldspar and quartz-moissanite aggregates as an example.