Kaszab Zoltán (szerk.): A Magyar Természettudományi Múzeum évkönyve 65. (Budapest 1973)
Embey-Isztin, A.: On the problem of graphic intergrowth and normal granitic structure
ANNALES HISTORICO-NATURALES MUSEI NATIONALIS HUNGARICI Tomus 65. Budapest 1973. On the Problem of Graphic Intergrowth and Normal Granitic Structure By A. EMBEY-ISZTTN, Budapest Abstract — A number of structural evidence have been found for a submagmatic, metasomatic origin of graphic-granopbyric quartz in the aplitic microgranite of the Székesfehérvár quarry. Transition phenomena between graphic and xenomorphic quartz of normal granitic structure, as well as the frequency distribution of relative positions of the c-axes of xenomorphic quartz to the c-axes of adjacent potash feldspar crystals indicate that metasomatic processes are involved in their genesis. Metasomatism has to be assumed also in the genesis of some of the aplite dikes in the Velence Hills. In spite of the numerous studies of pegmatites, granites, granophyres etc. exhibiting graphic structure, their origin is as yet rather disputed. Without going into details and mentioning only the most extensive studies in this field, one might say that two essentially different kinds of interpretation exist. The first one, in choronological order, is attributable to FERSMANN (1928). He interpreted the intergrowth as an eutectic fabric originating from the simultaneous growth of quartz and feldspar. On the other hand, DRESCHER-KADEN (1948) and AUGUSTITHIS (1962) think that, instead of a simultaneous crystallisation, a subsequent metasomatic resorption of feldspar by quartz and vice-versa take place. The difference of opinion seems to form a part of the general dispute on the granite problem, since petrologists standing nearer to the pure magmatist school will likely support the first theory, whereas transformists the second one. Until the question remains open any further data may be of great use. That is why w T e publish our observations on the micrographie fabrics of the aplitic microgranite and aplite occurring in the Székesfehérvár quarry (Velence Hills, Hungary). Structure analysis At the present state of our knowledge the aplitic microgranite of the Székesfehérvár quarry can be regarded as a fine grained border zone of the Velence granite area. Signs of submagmatic, autometamorphic processes, such as graphic structure, ttirmalinization, pegmatitic nests, were first described by VENDL (1923). As regards the Velence basal granite, all authors are unanimous in favor of an intrusive magmatic origin (VENDL 1914, JANTSKY 1957, GOKHALE 1965, BUDA 1969). Graphie structure is very rare in the basal granite; on the contrary, it is remarkably abundant in the aplitic microgranite. As a matter of fact, we can speak about micrographie structures, since the phenomena cannot be examined save under the microscope. Among the parts of a micrographie character, there is a normal granitic structure. The frequency of micrographie parts is variant. Sometimes three or even more of them occur within a thin section. Although graphic intergrowth quartz/^-feldspar is predominant, graphic intergrowth quartz/oligoclase is not rare at all (Plate I Fig. 1,2). There are -[Darts characterised by real graphic Ann. Hist.-nat. Mus. Nat. Hung., 1973, 60
