Badania skaleni andezytów pienińskich (w celu wyjaśnienia dwuznaczności przy wyznaczaniu osi bliźniaczej metodą Fiodorowa) oraz własności optyczne kierunku C

Abstract

INVESTIGATIONS OF THE FELDSPARS OF PIENINY (CARPATHIANS) ANDESITES (IN ORDER TO EXPLAIN THE AMLIGUITY IN THE DETERMINING THE TWINNING AXIS BY FEDOROV'S METHOD) AND THE OPTICAL PROPERTIES OF DIRECTION COn the feldspars of the Pieniny andesites the author has analyzed various alternatives as to the cause of the ambiguity in determining feldspars by Fedorov's method. These ambiguities may be divided into 2 kinds: those that are connected with the approach of a pair of analogous optical vectors of both twin individuals, appearing in add feldspars, and those connected with the method of directly determining the twinning axis. The author proposes the use of triads. In order to avoid errors indirect determination of the twinning axis she pays attention to the two already known directions, i.e. the main direction H and the second direction C, set at right angles to the former and to the twinning axis B; both directions H and C show, when aligned with axis A5 (for H) or axis A4 (for C), similar optical properties as axis B. More accurately the author investigated instances when it was possible to mistake axis B for direction C; furthermore, she reports her attempt of theoretically explaining the optical properties of direction C. This explanation she based on an analysis of Fresnel's equation for the intensity of light passing through crossed nicols and a birefringent plate placed between them: J = J0 sin2 2ϕ sin2R . This equation consists of 2 functions which are so evidently adapted to the sections of the twin which are parallei to directiorn C, that the intensity of light passing through them ls alike. The unicolourness must be ascribed to the physiological properties of the human eye registering, as being ostensibly identical, colours which, although but very little, are non-identical, and which are both saturated with "blackness" to such extent that they appear to be identical.