ISSN 00201685, Inorganic Materials, 2011, Vol. 47, No. 6, pp. 633–636. © Pleiades Publishing, Ltd., 2011. Original Russian Text © I.Z. Babievskaya, N.F. Drobot, S.V. Fomichev, V.A. Krenev, 2011, published in Neorganicheskie Materialy, 2011, Vol. 47, No. 6, pp. 709–712.
Evaluation of the Mineralogical Composition of Gabbro Rocks from Chemical Analysis Data I. Z. Babievskaya, N. F. Drobot, S. V. Fomichev, and V. A. Krenev Kurnakov Institute of General and Inorganic Chemistry, Russian Academy of Sciences, Leninskii pr. 31, Moscow, 119991, Russia email:
[email protected] Received May 24, 2010; in final form, September 30, 2010
Abstract—A procedure proposed earlier for calculating the mineralogical composition of basalts from chem ical analysis data has been developed further. We have calculated the mineralogical compositions of various gabbro occurrences in Russia. The calculation results correlate well with earlier data on the mineralogical composition of the rocks in these occurrences. DOI: 10.1134/S0020168511060021
INTRODUCTION As shown previously [1], the mineralogical compo sition of basalts can be inferred from chemical analysis data through physicochemical calculations. At the same time, gabbro rocks are widely used, along with basalt, as raw materials in the production of stateof theart thermal insulation materials, basaltreinforced plastics, and cast stone. Occurrences of gabbro rocks in Russia include gab bro, diorite, and transition varieties (gabbro–diabase and gabbro–norite) [2]. To exemplify the calculations in question, the fol lowing occurrences were chosen [2]: Maletinskoe, 1
Altai krai (gabbro–diorite); Golodai Gora, Karelia (gabbro–diabase); Bazhenovskoe, Sverdlovsk oblast (gabbro); Berezovskoe, Sverdlovsk oblast (gabbro); Pritrassovoe, Magadan oblast (gabbro); Malye Klyu chi, Primorskii krai (gabbro–norite); Dzamarashs koe, North Ossetia–Alania (gabbro–norite); and Novosmolinskoe, Chelyabinsk oblast (quartz diorite). PHYSICOCHEMICAL CALCULATIONS The rocks in the occurrences under consideration usually consist of the following minerals and mineral species: Plagioclases are represented by the alkalineearth feldspar anorthite (Ca[Al2Si2O8]) and the alkali feld spars albite (Na[AlSi3O8]) and orthoclase (K[AlSi3O8]). According to the percentage of anorthite, the following compositions are distinguished (%): 0–10, albite; 10–30, oligoclase; 30–50, andesite; 50–70, labrador; 70–90, bytownite; and 90–100, anorthite. 1
There is a misprint in [2]: the Maletinskoe occurrence contains gabbro–diabase [3].
Pyroxenes are represented by orthorhombic mag nesium–iron minerals of the enstatite–ferrosilite (MgMg[Si2O6]–FeFe[Si2O6]) series; monoclinic cal cium minerals of the diopside–hedenbergite (CaMg[Si2O6]–CaFe[Si2O6]) series; and sodium and sodium–calcium minerals: aegirine (NaFe[Si2O6]), aegirine–diopside, and aegirine–hedenbergite. The pyroxenes form a solidsolution series, socalled aug ites (Ca(Mg,Fe,Al)[(Si,Al)2O6]), which are most fre quently represented by a mixture of diopside and hedenbergite (usually with aegirine impurities). Olivines are minerals of the forsterite–fayalite (Mg2[SiO4]–Fe2[SiO4]) isomorphous series. Magne sium olivines containing 10–15% fayalite are the most widespread. Volcanic glasses consist of solidified magma that did not crystallize because of the rapid cooling. Volca nic glasses are amorphous and consist mostly of quartz and plagioclases. Metallic and accessory minerals, including magne tite (Fe3O4). In selecting the temperature range and atmosphere to make calculations for, we proceeded from the fol lowing: According to Yoder and Tilley [4], the temperature of liquid lava and that of the lava fountain during an eruption are 1000–1200°С. The exact lava crystalliza tion temperature in nature is unknown. A rough esti mate from temperature measurements in viscous lava (in a well through the lava lake’s solid crust) yields 1057–1065°С [4]. Based on these data, calculations were made for the range 900–1200°С (1170–1470 K). Equilibrium cannot be reached in lava being ejected [4] and sets in in the Earth’s atmosphere at a oxygen partial pressure of 20 kPa. Issues pertaining to the presence of water were addressed by Yoder and Tilley [4]: “A basaltic magma which crystallizes at or
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Table 1. Chemical composition of occurrences Weight percent Occurrence Maletinskoe Golodai Gora Bazhenovskoe Berezovskoe Pritrassovoe Malye Klyuchi Dzamarashskoe Novosmolinskoe
SiO2
Al2O3
TiO2
Fe2O3
FeO
CaO
MgO
K2O
Na2O
45.21 53.10 46.80 47.44 48.64 47.66 47.98 56.61
18.98 12.62 16.96 16.56 17.31 13.52 15.97 15.82
1.61 2.80 – 0.35 1.35 0.37 2.10 1.18
6.98 7.50 5.50 1.55 2.35 9.21 1.25 3.52
5.57 7.76 8.08 4.95 7.67 – 8.60 5.09
11.08 7.49 10.01 12.10 8.56 11.68 8.23 6.75
3.91 2.46 6.34 11.55 7.12 12.20 7.10 6.38
1.09 1.90 0.61 0.15 0.88 0.21 1.09 1.84
2.09 1.35 2.98 1.50 2.99 1.79 3.60 1.02
Table 2. Mineralogical compositions evaluated from chemical analysis data Calculated content of minerals and mineral species, wt % Minerals and Maletinskoe mineral species gabbro diabase** Anorthite Albite Orthoclase Diopside Aegirine Enstatite Forsterite Fayalite Quartz Magnetite Plagioclases Pyroxenes Olivines Ilmenite
42 15 7 12 2 5 – – 3 11 64 19 – 3
Golodai Gora*
Bazhen ovskoe*
gabbro diabase**
gabbro**
gabbro**
gabbro**
gabbro norite**
gabbro diorite**
quartz diorite**
23 12 11 12 – 1 – 1 22 13 46 13 1 5
32 26 3 15 – 4 4 6 – 10 61 19 10 –
39 13 1 18 – 17 3 4 – 4 53 35 7 1
32 26 5 9 – 13 1 6 – 5 63 22 7 3
29 16 1 24 – 11 7 8 – 3 46 35 15 1
24 32 7 14 – – 8 7 – 3 63 14 15 5
34 9 11 – – 16 – 2 19 7 54 16 2 2
Berezovskoe* Pritrassovoe*
Malye Klyuchi*
Dzama Novosmolin rashskoe* skoe*
* Occurrence. ** Occurrence type [2].
near the surface as basalt must have lost its water dur ing its course to the surface or was essentially dry ini tially.” In our calculations, we used the TERRA2003 pro gram system [5]. The thermodynamic database inte grated into this system, with corrections made by us, contained more than 50 minerals, which were included in the calculation as potential components. The chemical compositions of the occurrences under consideration were taken from [2] (Table 1). The cal culation results are presented in Table 2.
RESULTS AND DISCUSSION A criterion for the expediency of using physico chemical calculations is the reliability and accuracy of results in comparison with experimental data. The accuracy of thermodynamic constants varies from mineral to mineral. For some minerals, it is beyond doubt, and for some it is insufficient for obtaining reli able results. In our case, for most substances taken as potential mineral phases the accuracy in thermodynamic prop erties is sufficiently high, and possible errors cannot INORGANIC MATERIALS
Vol. 47
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2011
EVALUATION OF THE MINERALOGICAL COMPOSITION OF GABBRO ROCKS
lead to significant changes in the mineralogical com position of the rocks under consideration. No data on the mineralogical composition of the occurrences in question are available in the literature. In connection with this, the calculation results were compared to the known mineralogical compositions of their constituent rocks. Such data were taken from [6–8] are presented below in concise form. In conformity with the division of magmatic rocks into groups differing in silica content [6], they are divided into ultrabasic (
