Amethyst

Over the last 25 years, the gem industry has seen an increasing number of reports by associates and laboratories indicating a tremendous proliferation of synthetic quartz at all levels of the market. The stones reported were most often of the finest colors and with excellent clarity, often eye-clean. In recent years, there has been more material seen in colors without a natural counterpart.

ÖZET Balıkesir-Dursunbey-Gügü köyü (Batı Anadolu, Türkiye) kuzeyinde yer alan dasidik, riyodasidik Neojen yaşlı volkanik kayaçların boşluklarındaki ametist oluşukları, mikroprob, IR (kızılötesi) spektrum yöntemi kullanılarak incelenmiş, ayrıca gemolojik özellikleri saptanmaya çalışılmıştır. Ametist kristalleri, ana kayacın soğuma çatlak ve boşluklarında, bakışımlı veya bakışımsız damar ve boşluk dolgusu (jeod) şeklinde, faylanmayla oluşmuş breşik zonlarda ise küresel veya yarı küresel veya kenet biçimli yer almaktadır. Açık leylak, mor ve koyu mor renkli ametist minerali yüzeyde küçük, daha derinde ise iri kristaller halindedir. Kristal boyutları 1 mm. 'den 7 cm. 'ye kadar değişmektedir. Saydam kristallere rastlanmakla birlikte, çoğunlukla bulutumsu safsızlıklar içermektedir. Al, Ca, K, Cl elementlerinin yanı sıra, iz olarak Fe, Li, Mg, Mn ve Sb elementleri bulunmaktadır. Ametist mineralinin renklenmesinde; yalnız Fe elementinin değil, Sb ve düşük radyasyonun rol oynadığı, Kalsedon ve diğer kuvars oluşumlarıyla geçişli biraradalıkları gözlenen ametist kristallerinin düşük ve orta hidrotermal koşullarda ve değişik zamanlarda oluştuğu sonucuna varılmıştır. IR spektrum ölçüm sonuçlarına göre; karakteristik pikler 455 ve 780 cm-1 , kuvvetli Si-O-Si büklüm pikleri 455 ve/veya 500 cm-1 , Si-Si gerilim pikleri 600, 710 ve 780 cm-1 , geniş Si-O gerilim piki 825 cm-1 ve geniş O-H bandı 3150 , zayıf olarak da 3650 cm-1 dalga değerlerinde bulunmaktadır. Saydam ametist kristallerinden, takıda kullanılacak özellikte faset veya kaboşon kesim yapılması; jeod ve diğer biçimli olanların ise koleksiyon minerali olarak değerlendirilmesi düşünülmelidir. ABSTRACT Where crystals of amethyst occur is studied by using the microprobe and IR(infrared) spectrum methods. They were filled in dasidic and rhyodasidic volcanic rocks Neogene aged (Gügü village-Dursunbey-Balıkesir) and their gemological features are tried to be defined at the same time. Crystals of amethyst occur as symmetric or asymmetric filling in vein and geode , hemisphere or semi-hemisphere and clamp form in the brachia zone in which they developed by faulting. Amethyst crystals, which were obtained in upper zone, are pale lilac in colour due to sunlight but purple and the darker purple in colour and the larger crystal size in the deeper zone. The crystal size of amethyst varies from 1 to 70 mm. in size. Usually it includes some cloudy inclusions .It contains as trace elements; Fe, Li, Mg, Mn and Sb besides Al, Ca, K, Cl elements. Not only Fe but also Sb element and low radiation are valid in colouring Gügü's amethyst. It is observed that amethyst with or without chalcedony and other quartz occurrences several times and hypo or mesothermal stages of hydrothermal conditions. In the IR spectrum amethyst has diagnostic peaks at 455 and 780 cm-1 , also intense Si-O-Si bending peaks are observed at 455 and/or 500 cm-1 , Si-Si streching peaks at 600, 710 and 780 cm-1 , broad Si-O stretching peak at 825 cm-1 , broad OH-band is seen at 3150 and weak band at 3650 cm-1. Transparent crystals of amethyst should be cut facet or cabochon in form for jewelry, geode or other form of amethyst should be utilized as collection mineral.

Over recent decades, numerous studies have highlighted the importance of opal, chalcedony and quartz varieties, chiefly in volcanic, but also in metamorphic and sedimentary environments. The focus is to define accurately their structures, composition and properties, as well as to identify the factors controlling the formation and the ageing ofdifferent forms of silica. In the field ofarchaeological sciences efficient discriminants are the bases from which the origin and provenance of materials may be traced. Substantial efforts were made in the attempt to combine geochemical, mineralogical, petrographic and geological features with archaeological and archaeometric information. However the results show that data integration is complicated, and several unanswered questions remain. On the one hand, archaeological research has focused on technological and ethnographic aspects, mainly concerning use-wear and heat-treatment studies. Mineralogical characterization has often been limited to the identification of the material, frequently by Raman microspectroscopy alone. On the other hand, the Earth sciences have provided basic mineralogical, crystal-chemical and geological knowledge, but failed to provide a systematic data collection of sources and their geochemistry. As a consequence, large gaps persist in the identification of archaeological opals, chalcedonies and quartz varieties, and in the geographic mapping of possible sources. In this context, the present review aims to summarize the current academic debate on such issues, possibly to encourage further work in the field. After a brief introduction to terminology, the structure of opals, their colours and properties are discussed, followed by an introduction to silica dissolution/precipitation and opal-formation processes. The next section reviews the information available on use of opals and provenance from historical sources, mainly Pliny the Elder, followed by a short list of ancient and modern opal supply areas, together with a (necessarily incomplete) summary of the geological and geochemical information. The discussion then encompasses chalcedony, agate and chalcedony varieties (carnelian, sard, onyx, sardonyx, chrysoprase, Cr-chalcedony, ‘gem silica’ or ‘chrysocolla chalcedony’ and heliotrope), following the same scheme as was adopted for opals. Terminology, distinguishing features, formation conditions, information derived from Pliny’s books, past and current supply areas and, finally, archaeometric provenance issues are addressed for each type of material. As for chalcedony, a comprehensive note on moganite has been included. The nextsection focuses onchert, flintand jasper. Given the large amountof materials available on this topic, the present review must necessarily be considered introductory and partial. The discussion aims to provide useful indications on how to distinguish chert from flint and chert from jasper; secondly, the information provided by Pliny and the archaeometric state of the art on these materials is reviewed.
The last section examines quartz varieties: hyaline quartz (rock crystal), milky quartz, smoky quartz, rose and pink quartz, amethyst, citrine, prasiolite and blue quartz. An exhaustive mineralogical discussion on quartz is beyond the scope of this review; conversely a review of the historical information is provided, together with a brief list of major supply areas, a summary of the archaeometric studies performed on these materials, as well as an indication of the geological literature which can be used proficiently for provenance studies.

SUMMARY: Lecture 12 discusses the end of Early Minoan period, the rise of Middle Minoan period, and the emergence of palace centres on Crete. This lecture is designed mainly as an educational resource for college students (i.e., normally posted only on my institution's course website), the public (e.g., people auditing my course), and interested colleagues from other disciplines (to whom I provide copies privately).  I am posting it here, both as a broader access, educational tool, and especially to promote the study of this region and its past societies.  For further knowledge about this region and period, I refer interested parties to the textbooks and other sources from which the materials were extracted (see syllabus), and/or the bibliographies in these works and my online resource guides (see other files in my academia folders).  The lecture summarizes the pertinent materials in the course textbook(s), adding in other data, and furnishing numerous images to clarify information encountered within the textbook(s).  Some generic imagery (usually indicated as such) is posted to aid in transmitting various concepts visually, and/or when a specific image remains not located (temporarily).  I update and revise such lectures each time, with such elective courses normally being taught once every two years.  I try to cover the most current, mainstream views, and usually place summary notes at the end of each lecture alongside some of the key sources used for compiling the ppt.  Over time, each lecture is improved, errors rectified, and additional data placed within the lecture.  These ppt. lectures take many hours to compile, but they have proved useful to many of my more serious students and I hope they can be of benefit to others as well.  My apologies for any errors I may have made, and my liberal usage of educational imagery from professional sources and vetted internet sources. REVISED: Feb., 2024: Some new formatting, revised text, images, etc.

В издании публикуются материалы научной конференции, прошедшей 20-22 ноября 2013 г. в Москве. В докладах участников конференции поднимались вопросы экономики, хозяйства, военной истории, духовной и материальной культуры России XVI-XVIII вв. Книга предназначена историкам, археологам, студентам исторических специальностей и всем интересующимся историей России.

Amethyst may develop into the more common
citrine and rarer green quartz naturally under certain
geologic conditions. On the California-Nevada
border, just north of Reno, amethyst, citrine, and
green quartz do occur together in clusters of crystals
in detritus. These crystals, found lying loose in rocky
and sandy rubble, appear to have eroded from
cavities and vesicles in the inaccessible cliffs above.
The quartz was deposited in these spaces by the
slow acc~~mzllatioonf silica jrorn migrating
solutions. Low-grade radiation over a geologic time
span was responsible for the alteration of the ferric
and ferrous quartz into its amethystine color.
Secondary, high-temperature, extruding volcanic
bodies are believed to be responsible for the
subsequent color change to citrine or green quartz.

I have always been fascinated with and almost in awe of crystals and gemstones. As a child I never got into collecting dolls or toys; I collected rocks! My rock collection was quite impressive; I had crystals and geodes from all over the world. ☺ Crystals have been used for a variety of purposes for thousands of years and over the last 30 years or so people have been using them for healing purposes. My first introduction to the power of crystals was at a crystal workshop where I learned:

Epithermal-altered volcanic rocks in Greece host gem-quality amethyst veins in association with various silicates, carbonates, oxides, sulfides and halides. Host rocks are Oligocene to recent calc-alkaline to shoshonitic lavas and pyroclastics of intermediate- to acid composition. The amethyst-bearing veins occur in the periphery of porphyry-type and/or high-sulfidation epithermal mineralized centers in northern Greece (e.g. Sapes, Kirki, Kornofolia/Soufli, Lesvos island) and on Milos island in the active Aegean Volcanic Arc. Hydrothermal alteration around the quartz veins includes sericitic, K-feldspar (adularia), argillic, propylitic and zeolitic types. Precipitation of amethyst in the northern Greece occurrences, took place during the final stages of the magmatic-hydrothermal activity from near-neutral to alkaline fluids, as indicated by the presence of gangue adularia, calcite, smectite, chlorite, sericite, pyrite, zeolites (laumontite, heulandite, clinoptilolite), analcime and ...