Dr. Nagy I. Zoltán szerk.: Fragmenta Mineralogica Et Palaentologica 4. 1973. (Budapest, 1973)

_ 0.44739 i» + 0.81747 k» - 0.47672 £» + 0.12806 k' + 0.75527 + 0.56188 k» The twinning axis 1 is transformed into the system X* Y' Z' X' = - K

x Y» = - U Z» = Z 1» = - 0.86448 i» - 0.50222 £» + 0.00428 k' The Goldschmidt values: & = 239.85° P= 89.73° Consequently the twinning axis of the twin members B and E coincides with the (110) face normal (inversion centre), i.e. it is the twinning law according to (110). The Goldschmidt values interpolated to 75 per cent anortite content into the (110) face: 0 = 59.9° P = 90°. Plagioclase Twins Occurring in the Börzsöny Mountains Fifth twin crystal Sign of the rock sample: Nm.28

e Natural exploration of andésite agglomerate can be found in the margin of the village Nagymaros, in the Templom valley. The light grey andésite, the measurement data of which are introduced, derived from this place. This andésite possesses twin crystals of oblique composition. The texture of the rock is porphyric-microlitic, the major part of the feldspar phenocrysts predominating among the porphyric components is of 600 to 900 n size. The measurement data of the plagioclase grain shown in Fig. 6. as well as the co-ordinates of the unit vectors are as follows: a» = - 0.36457 i» ~

B

o hi = + 0.86961 i» "

B

o c' = + 0.33456 i»