Геммология и камень в архитектуре
PRECIOUS NATURAL STONES Fiora L., Costa E., Alciati L
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- Chemical content of some elements in onyx samples
- NEW DATA ON PRASIOLITE
PRECIOUS NATURAL STONESFiora L., Costa E., Alciati L.Dipartimento Scienze Mineralogiche e Petrologiche Università, Turin, Italy, fiora @dsmp.unito.itNatural stones, that is the intrusive, effusive, sedimentary and metamorphic rocks employed as architectural materials, are now offered on the international market in thousands of varieties which come from all parts of the world. As a rule they are marketed in the standard form of massive parallelepipedal blocks (approximate dimensions: 2.70–3.001.40–1.601.40–1.60 m ) or as slabs obtained by block sawing. Colour and pattern are the aesthetic features conditioning the users’ choice. The production of marble, granite and stone, all over the world has settled at about 55,000,000 tons/year [5]. China and Italy are the current main producing countries. Among nowaday natural stones, also gemmologic materials have to be included and they are much valued because of their rarity and uncommon colouring. Often marketed as blocks of smaller size, they may exceptionally be found on the market as slabs, or blocks, of regular shapes : for instance this is the case of sodalite pegmatites (Sodalite Blue Bolivia), sodalite sienites (Azul Bahia from Brazil and Blue King from Zambia), amazonite bearing sienogranites from Malawi (Amazonite), from Brazil (Evergreen), from Kazachstan (Maikulsky), “calcareous alabasters” mined in Pakistan, Egypt, Iran, Mexico. Malachite is a mineral much valued as a decorative material, already used in the past for ornamental purposes. Now it is usually re-proposed in the form of “re-assembled “ slabs made of fragments of decimetric size stuck together: the samples currently employed as natural stone are from China and Zambia. Blue calcite (Azul Cielo Marble, from Argentina), silicified wood (Madagascar), fuchsite (Madagascar and Brazil) are further examples of precious materials now used also for flooring and tiling, mostly in the form of tesseras and inlay. They are as well used for works of engraving, cabinet and furniture making and at times for sculptures. Onyx marbles (Oriental Alabaster), namely “ calcareous alabasters”, form a class of much prized ornamental stones. They were sought for and used since the ancient times owing to their aesthetic characteristics (colour and translucency) and, besides, to their easy workability. The latter property was exploited for the creation of artistic manufacts of various kinds. The deposits are widespread; however quarrying is profitable only for some of them since, quite often, the layers formed by precipitation are too thin. As regards Europe, virtually all these deposits were exploited to exhaustion in the past. In Italy, for example, several sites of hystoric interest are known. Also Algeria, Morocco and Tunisia yielded in the past many varieties of onyx marble [1], and the corresponding works of art are to be found in the Mediterranean area. In Egypt the local onyx, called Ancient Egyptian Alabaster and named by Pliny Alabastrites or Lapis Onhyx , was worked since the ancient times and largely used by the Egyptians in architecture and sculpture [3]. The Romans as well used it in carving columns of medium and small size, facing and decoration, but also in sculpturing urns, vases and other vessels and statues. It is still quarried. In the past, deposits in France and Spain were the source of a number of varieties of onyx marble while outside Europe Mexican varieties are worth mentioning, particularly Pedrara onyx . Other extra-european onhyx marbles now marketed are from U.S.A. (Arizona, California, Colorado, Utah, Virginia), Argentina (Onyx Aurora and Onyx Virginia), Bolivia, Peru (Nacarado Green Onyx, Yellow Onyx), Uruguay. A white variety from Brazil is known. In Asia Iran is the producing country of several varieties: they are marketed under various names and show quite a gamut of tints from reddish to yellowish to green and white as well.Currently these Iranian stones are of great weight in the international market (table). Large bodies occur in Afghanistàn, connected to the Iranian and Pakistani ones , whose extension id estimated to be at least 2,500 km2 ; however the politic and economic situation leaves this country out of the producers’ group. Of Pakistani origin are both a white onyx and a more renowned and used green variety. The Pakistani deposits [4] are located North of the Baluchistān desert, along the Iranian–Afghanistàn border ; however there are widespread outcroppings in all three countries. The genesis of these deposits is relatable to an extended pleistocene volcanism that involved the pre-exsisting carbonatic Himalayan rocks. The dissolution of the latter ones, and the subsequent precipitation of calcium carbonate, originated the onyx which, in the outcroppings, intercalates to the volcanites. Pakistani onyx in most cases shows lentiform masses, less often veins. The Pakistani material may be found in the market as White Onyx, Light and Very Light Green Onyx, Medium Green and Dark Green Onyx, the last a rare variety showing homogeneous patterns. The discovery and exploitation of the more important deposits ( Mashki Chah west, Zeh, Chilgami, Patkok ) dates from the sixties only, but the employment of this onyx is already widespread. From Namibia comes an onyx marble known as “ aragonite” [6]. The colour of onyx marble greatly varies according to the impurities that are present; even the samples from a given quarry may show different colouring. Alabastrite, when pure, that is to say formed of calcium carbonate alone, is white; however the rock may show the whole gamut of the solar spectrum: blue, green-blue, green, yellow, pink, red and also brown or black. The colouring is usually relatable to the presence of iron , which gives rise to different tints as a function of its percentage and oxydation state. In literature , at times, the green colour is attributed to some other chromophoric element: for instance [4] ascribes the green colouring of Pakistani onyx to the presence of copper. At the Dipartimento di Scienze Mineralogiche e Petrologiche of Turin University, in order to clarify the cause of colouring, a chemical characterization has been carried out by the spectrometric plasma optical emission technique (ICP–AES) using the IRIS II Advantage/1000 Thermo–Jarrel Ash Cor. instrument. The samples were taken into solution by nitric acid attack (about 1 g of sample totally dissolved in concentrate acid, and lead to 50 ml volume with 18MΏ deionized water). It turned out that the green colour of Pakistani onyx is due to high iron content. As regards the Emerald Iranian Onyx , the bright green zones have larger contents of copper and iron whilst the dark green ones are richer in manganese and copper. The yellow and brown colouring in the Egypt Onyx are ascribable to dispersed iron (table). Table Chemical content of some elements in onyx samples
Pattern is the remaining more important commercial feature. It greatly changes whether the rock has been cut to bedding or cut to hard way. In the former case the winding, roundish, textures are evidenced and this apparently is the pattern more liked; in the latter case the alternation of parallel layers with different colouring stands out. References: 1. Blanco G. Dizionario dell’architettura di pietra. Carocci Roma, 1999. 300 pp. 2. Fiora L., Esbin M. Sculture in pietre ornamentali // Marmor, 2001. V. 72. P. 9–21 (Zusi editore). 3. Kempe D.R.C., Harvey A.P. The Petrology of Archeological Artefacts. London: Clarendon Press, 1983. 4. Nilo Milocco A. Gli onici del Pakistan // Marmi Pietre Graniti, 1977. 18. 97. 73–98. 5. Primavori Piero. Planet Stone. Zusi Ed. Verona, 1999. 326 pp. 6. Webster R. Gemme. Zanichelli Editore Bologna, 1994. P. 382–385 NEW DATA ON PRASIOLITESachanbinski M., Jezierski A.University of Wroclaw, Wroclaw, Poland, msach@ing.uni.wroc.plGreen quartz, also called prasiolite or greened amethyst, is produced when amethyst from certain localities (Four Peaks, Arizona; Montezuma Mine, Minas Gerais, Brazil, Zambia) is heated between 300 and 600C [3]. Prasiolite characteristic feature, differentiating it from green, crystalline quartz with irradiation — related colour, is the presence, in its optical spectrum of absorption band 725–740 nm (13 800–13 500 cm–1), the so called “green absorption band” related to Fe2+ ions occurring in interstitial distorted octahedral sites J6 of the quartz structure. At present there are green, transparent varieties of Fe–bearing synthetic quartz known, which colour is conditioned by the presence of absorption band 740 nm (13 500 cm–1) and caused by non-structural admixture of colloid-dispersed aggregates or gel [1, 4]. For the first time a natural occurrence is described. It occurs in trachybasalts (mandelstones) in the vicinity of Suszyna-Mrówieniec near Klodzko and Plóczki Górne near Lwówek Slaski in Lower Silesia [2]. Trachybasalts (mandelstones) related to the third sedimentary-volcanic cycle are covered by sandy-clay sediments; within these sediments occur trachybasaltic blocks of various size, containing quartz-agate geodes with diameters of few mm to 10 cm. The groundmass of these geodes is colourless quartz, occasionally light-violet amethyst and olive-green prasiolite. In all investigated prasiolite samples the paramagnetic centres were detected. At low microwave power (0.1 mW) the E' centres may be easily detected; however, for the investigated power samples the E'1 , E'2 etc. centres cannot be distinguished. At microwave power 20.0 mW the E' centres give weak signal about g=2.0004; the stronger signals are attributed rather to paramagnetic forms of oxygen. The all detected centres have radiation nature, although the E' centres and possible peroxy centre are intrinsic defects in contrast to the impurity-related centres connected with presence of Al3+ or other metal ions in quartz lattice. The signal at g=2.0037 and 2.0075 are the strongest for olive-green prasiolites from the Kaczawskie Mts.; the signals characteristic for green quartz from Plóczki Górne are 10% smaller; the signals for samples from Suszyna are 50% smaller. The signals are connected with paramagnetic forms of oxygen (0-) interacting with Al3+, Fe2+ and alkali metal ions (Na+, Li+); the signals at 2.022–2.018 are due to the last type interaction. The intensity of the signals at g=2.0075 and g=2.0037 is reduced after 1 h annealing at 500 K; 10 h annealing at 500 K leads to appearing of the broad-line signal characteristic for Fe3+ at g=2. Although the EPR spectra of prasiolite and smoky quartz are very similar, the broad line characteristic for Fe3+ is detected after annealing only in case of prasiolite. This phenomenon suggests the possibility of the interaction of Fe2+ with 0– in prasiolite and formation of the pair Fe3+ – O2– after annealing. It is fully reliable, that prasiolite colour of natural quartz crystals is not connected with amethyst colour but its nature is primary one. It appears that colour of prasiolites and amethysts as well as Fe centres, reflecting well defined Fe-colour centres state in structure of quartz, is the result of specific combination of physical and chemical parameters in quartz forming solutions. Taking into account the geological position of trachybasalts with prasiolite occurrences, which belong to the last sedimentary-volcanic cycle and were not influenced by strong temperature activity it is hard to imagine the secondary nature of prasiolite. References: 1. Балакирев В.Г., Киевленко В.И. Минералогия и кристаллофизика ювелирных разновидностей кремнезема. М.: Недра, 1979. 148с. 2. Platonov A.N., Sachanbinski M. at al. // Z.Dt. Gemmol. Ges., 1992. N 1. P.21–27. 3. Rossman G.R. // In: Reviews in Mineralogy, 1994. V. 29. P. 447–448. 4. Самойлович М.И., Цинобер Л.И. и др. // Докл. АН СССР, 1969. Т. 182. № 1. Р. 91–93. A Alciati L. 58 Aurisicchio C. 55 C Corami A. 55 Costa E. 58 Cozar J.S. 56 F Fiora L. 58 G Gavrilenko E.V 56 J Jezierski A. 60 N Nunziante-Cesaro S. 55 S Sachanbinski M. 60 А Аксенов Н.А. 48 Алферова М.С. 2 Ананьев С.А. 3 Ананьева Л.Г. 22 Ананьева Т.А. 3 Антонио Ф.Г. 4 Антонова Е.И. 27 Б Бакшеев И.А 31 Баранов П.Н 7 Баранов П.Н. 4, 6, 8, 54 Бартоломеу А.Д.П 8 Бахтин А.И. 28 Богомолова Е.В. 32 Бокайло С.П. 10 Брусницын А.И. 11 Буйко А.А. 14 Буйко А.К. 14, 53 Булах А.Г. 16, 17 В Викторов М.А. 18 Владыкин Н.В. 41 Г Григорьев В.В. 23 Д Дехтулинский Э.С. 36 Е Евдокимов М.Д. 46 Елфимова Е.В. 19 Еремина Е.В. 26 Ермолаев Д.Н. 20 З Золотарев А.А 14, 16, 33 Золотарев А.А. 17 И Иванова О.А. 22 К Кальницкая Е.Я. 17 Качалин Д.В. 20 Клейменов Д.А. 23 Корзакова А.В. 24 Коровкин М.В. 22 Кузнецова Л.К. 25 Курбатов К.К. 29 Л Ланцев Я.Л. 18 Левченко Е.М. 26 Леонюк Н.И. 48 Лизун В.М. 38 Лобзова Р.В. 27 Лопатин О.Н. 28 М Марков В.И. 43 Марсий И.М. 27 Микоева Е.И. 10, 29 Михайлов В.В 31 Михайлов В.В. 31, 41 Михайлова А.В. 31 Н Нестеров А.Р. 53 Нечелюстов Г.Н. 44 О Озерова О.А. 31 Ольховая Е.А. 32 П Палкина Е.Ю. 49 Панина Л.К. 32 Полеховский Ю.С. 33 Пономарева Н.И. 19, 26, 31, 41 Потапов С.С. 35 Прокопец В.В 36, 38 С Саврасов С.И. 40 Савченок А.И. 16 Сахаров А.Н. 19 Седова Е.В. 41 Секерина Н.В. 42 Совлук В.И. 43 Сокол-Кутыловский И.О. 23, 45 Соколов П.Б. 19 Соколов С.В. 44 Сухаржевский С.М 32 Сухаржевский С.М. 46 Т Тимофеева Н.А. 46 Ф Фитцнер Б. 17 Фишман А.М. 47 Фролова Л.В. 26 Х Хайбуллин И.Б. 28 Хайбуллин Р.И. 28 Харина Н.А. 33 Хачатуров С.А. 48 Хоменко Ю.Т. 7 Хренов А.Я. 49 Ц Цоцко Л.И. 50 Ч Чернавцев В.С. 52 Чумаков И.С. 53 Ш Шевченко С.В. 54 Шелементьев Ю.Б. 18, 31, 40 Шурилов А.В. 33 Я Ярмишко С.А. 44 жүктеу/скачать 1.91 Mb. 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