NDM44_eng_09-11_091228:NDM44_02_pek_FMM_0909011.qxd 29.12.2009 18:27 Страница 97 New Data on Minerals. M., 2009. Vol. 44 97 THE ESSAYS ON FUNDAMENTAL AND GENETIC MINERALOGY: 4. EUDIALYTE-EUCOLITES AND PROBLEMS ON TYPOMORPHISM OF MINERALS Boris Ye. Borutzky Institute of Ore Deposit Geology, Petrography, Mineralogy and Geochemistry RAS, Moscow, [email protected] The present paper is a sequel to the previously published (Borutzky, 2008) essay on the minerals of variable com- position with variable structure (MVCVS) with an example of eudialyte-eucolites. The characteristic feature of this typical mineral from alkaline complexes is the unique ability to include up to one third of The Mendeleev’s Periodic Table of the chemical elements in its composition. This is entailed by a partial realignment of the crystal structure in response to changing chemistry and evolution of the mineral-forming environment with time. According to the author, the detailed typomorphous analysis of eudialyte-eucolites is more informative and use- ful in terms of genetic mineralogy rather than formal determination of dozens of independent mineral species. 3 tables, 48 references Keywords: eudialyte-eucolites, minerals of variable composition with variable structure. What is typomorphism and its issues natural chemical compounds, but worked towards determination of the relationship «We have to distinguish two types of between composition, structure, mineral prospecting features: one is related to the properties and conditions of formation, i.e. its nature of the objects sought for (minerals and genetic features in order to use them as the elements) that result from ion and lattice struc- mineralogical indicators for solving problems ture features. The second is related to an exter- of rock- and ore-formation. nal environment and determine factors due to The investigation of typomorphism is car- concentration of the chemical elements» ried out in different ways. Some scientists insist on the universal, global sense of the Alexander E. Fersman typomorphous features which in this case are the “rules” and not the “particular case”. The term “typomorphism of minerals” was These scientists often consolidate or gene - first introduced in 1903 by Friedrich Becke ralise the geological objects or deposits and (1855–1931), Austrian mineralogist and rock types without good reason. They are car- petrologist, the foreign corresponding mem- ried away by the “blind” mathematical statis- ber of the Emperor Petersburg Academy of tics, create comprehensive world-wide “data- Science. This problem was resumed in Russia bases” where only one specimen represents in the 1930s by Alexander E. Fersman. In the the Khibiny massif in whole, with no indica- 1970s the doctrine on typomorphism of miner- tion of the host rocks type, its location and als was created under the direction of Fedor conditions of formation. Such an approach to V. Chukhrov and other outstanding Soviet our point of view is a formal one. This hyper- scientists; and the talks on it were included in trophied “disadvantage” can be illustrated the Programme of XI IMA meeting held in with the following statement: “nepheline is a Novosibirsk (Scientific foundations.., 1980). typomorphous mineral of the nepheline sye - The fundamentals of this doctrine lie in obser- nites”, which is true but senseless for the fur- vations and revelations of the most typical ther application. (typomorphous) minerals, their associations On the other hand, some generalized the- or crystal and mineral morphology (typo-mor- sis are quite useful. For example, the occur- phous = “typical shape”), typical features of rence of b-quartz which cannot be formed a chemical composition, crystal structure and over 573°С (at normal pressure) or occurrence physical properties of a mineral. All these of microcline which stability field is below characteristic features have to correspond 500±50°С – are reliable geo-thermometers with the geological and physical-chemical applied to judging the temperatures of the (including kinetics) conditions of the geologi- rocks and ores formation. The point of inver- cal structures formation. In other words, Soviet sion a ® b in quartz was widely applied by mineralogy did not aim only to discover new Alexander E. Fersman for derivation of his NDM44_eng_09-11_091228:NDM44_02_pek_FMM_0909011.qxd 29.12.2009 18:27 Страница 98 98 New Data on Minerals. M., 2009. Vol. 44 geo-phases. The phase conversion sanidine ® The author in his investigations of mineral microcline1 has an important significance. typomorphism opposed a “formal” approach The presence of microcline, for instance, but advocated a maximum concrete defini- make conclusions on the high temperature tion. We called it (apparently poorly) “the formation of some microcline-containing concrete typomorphism” or “typomorphism agpaitic nepheline syenites, doubtful. Thus, of the minerals from the concrete geological according to the experimental data obtained objects”. We believe that the factors of the by Liya N. Kogarko (1977), the average melt- mineral-forming process, both external and ing temperature of the stratified rock complex internal (according to the statement by of foyaites-lujavrites-urtites from the Alexander E. Fersman, see epigraph) are Lovozero massif is 1070°C in dry conditions or diverse and their combinations within the spe- 910°C at P = 1 kbar. For the rock complex cific geological objects of different scale are H2O of eudialyte lujavrites these are 990 and 872°С also diverse (Borutzky, 1986; 1988; 1997). respectively. As microcline crystallisation was Thus, to specify an example with nepheline impossible at such a high temperatures, it is above, in order to compare different rock absolutely obvious that the mineral indicators types of the Khibiny massif – nepheline syen- were ignored. They indicate the post-crystalli- ites, melteigite-urtites, juvites and ristschor- sation transformations within these rocks, and rites we shall consider the typomorphous fea- the possibility of another (rather than direct tures and difference in the chemical composi- crystallisation from the melt) interpretation of tion of nepheline from the rock-forming a genesis of industrial rare-metal agpaitic nepheline. For comparison of different mineralisation in association with microcline, nepheline porphyres one should consider the was not considered. composition of nepheline phenocrysts and As pointed out before, the typomorphous matrix; and for the small bodies (for instance, features can be not only shapes of the crystals individual pegmatite veins or apatite- and other mineral formations (proper typo- nepheline ores with different structure etc.) morphism), but also peculiarities of the mine- and also consider the changing chemical com- ral chemical composition (typochemism) and position within the crystal growth zones. The crystal structure (structural typomorphism external and internal factors of the mineral- which we would like to name similarly forming process reflect the typomorphous “typostructurism”). From the critique articles peculiarities of the minerals in a different way. by my opponents (Rastsvetaeva, Chukanov, The external factors – geological, thermody- 2006; Rastsvetaeva, 2007) we find that “struc- namic and kinetic – determine the relation- tural typomorphism is a concept about the ship of the crystallised mineral with its envi- close relationship between fine peculiarities ronment – equilibrium progress, individual of the mineral crystal structure and conditions mineral growth rules, mineral chemical com- of its formation – the new and rapidly deve - position and the number of micro-impurities loping line of geological science”. At the XI allowed etc. Also they define the transforma- meeting of the IMA (Scientific fundamentals.., tion in morphology and properties of the mi - 1980) diverse research papers on structural neral in geological time scale in the post-crys- typomorphism were presented by V.A. Frank- tallisation conditions with the changed condi- Kamenetsky, V.A. Dritz, B.B. Zvyagin, tions of the mineral-preserving medium, i.e. A.P. Zhukhlistov, S.V. Soboleva, B.M. Shmakin, the phase transformations within the mineral, G.G. Afonina, M.T. Dmitrieva, O.V. Rusinova metamorphism, metasomatic replacements and V.L. Rusinov. The above mentioned effected by the late solutions evolved during examples of a ® b inversion in quartz and the change in geological conditions. The sanidine ® microcline transformation, are internal factors – is an ability of the mineral typical investigations on the structural typo- structure, as some sort of a “muzzle”, that morphism of these minerals, as they reflect restrains chemical diversity in the mineral at exactly “the close relationship between fine certain conditions, and (if it is possible) which peculiarities of the mineral crystal structure adjusts to possible chemical and physical- and conditions of its formation”. chemical changes of the mineral-preserving 1 – It is relevant to remind that the high-temperature phases can be metastable crystallised within the low-temperature pha - ses stability fields. But the low-temperature can not be crystallised otherwise. For instance, crystobalite transforms into try- dimite at low pressure and 1470°С, trydimite transforms into the high-temperature a-quartz at 870°С, and at 573°С a-quartz transforms into the low-temperature b-quartz. However crystobalite and trydimite often o ccur in o pal s a s gl o bul es. Th e meta sta bl e h igh -t emper at ur e po ta ssium sa n idin