gems, spinel, color in spinel, cobalt spinel, color change, alexandrite effect, color science

In gemmology, the term Alexandrite effect" is used to describe colour change phenomenon when a gemstone is observed under different light sources, usually between daylight and incandescent light. The definition of the Alexandrite effect is constantly being broadened with new discovery of gem resource. The traditional definition of the Alexandrite effect attributing the colour change phenomenon to the presence of two maximum transmission regions and a maximum absorption region in the absorption spectra. In this study, 7 blue spinels and 5 blue gemstones (including tanzanite, kyanite, fluorite, and 2 sapphires) showing the Alexandrite effect were investigated. The goal is to explain the cause of blue-to-violet alexandrite effect and the spectral features causing such colour change. In the UV-Vis spectra, all samples showed a maximum absorption peak in the range of 534-610 nm, within the green region to orange region. The traditional explanation of green to red Alexandrite effect required a transmission window in the red region; however, some of our samples did not show this transmission window and the blue-to-violet alexandrite effect was still visible. Therefore, it is incomplete to explain the mechanism of the Alexandrite effect according to their characteristic absorption spectra, a systematic study based on modern colour science and colour perception in human vision is required to elucidate the blue-to-violet alexandrite effect."

gems, corundum, USA.12, Montana.12, chemistry, geology.11, inclusions.5

A new, comprehensive approach to characterizing detrital corundum in sediments and placer deposits is outlined and applied to a sample of poorly sorted, mud-supported colluvium rich in rhyolite tuff clasts from the sapphire-producing layer at Gem Mountain Mine, Rock Creek, Montana. High angularity and the predominance of inherited surface features indicate that corundum was not abraded during transport, consistent with deposition by mass wasting. Corundum grain abundances per 10 kg of sediment (rounded to nearest whole number) are as follows: 4–8 mm (1 grain), 2–4 mm (12 grains), 1.0–2.0 mm (10 grains), 0.5–1.0 mm (43 grains), 0.25–0.50 mm (90 grains), 0.125–0.250 mm (480 grains), and <0.125 mm (55 grains; underrepresentation due to poor recovery). The ∼ 50× abundance of corundum in <2 mm size fractions relative to the >2 mm size fraction of potential economic interest suggests that fine-grained corundum may have potential as a pathfinder for gem corundum deposits in heavy mineral surveys. Corundum grains are transparent and divided into four types by surface texture and extent of crystal face development: (1) rounded with frosted surface, anhedral/subhedral; (2) angular with hillocky/irregular surface, anhedral/subhedral; (3) angular subhedral grains with glassy curved faces; and (4) angular, idiomorphic blue grains (all <1 mm). Surface texture Types 1–3 occur in pastel-colored corundum (green, yellowish-green, yellow, colorless) and are the result of dissolution subsequent to euhedral crystal growth. Mineral inclusions in corundum include: pastel corundum – biotite (variable Fe, Mg, Ti, F contents), plagioclase feldspar (andesine-labradorite), rutile, hercynite; blue corundum – alkali feldspar, rutile, zircon, ilmenite, apatite, spinel. Corundum uncommonly occurs in composite grains with biotite, plagioclase, and K-feldspar. Rhyolite occurs as a partial encrustation on one corundum grain. Rock Creek corundum may have originated from partially melted metapelite in a metamorphic basement, and incorporated and transported to the surface by rhyolitic magmas. Due to scant geologic context and an absence of radiometric age data, the proposed genetic model remains highly speculative.

gems, luminescence, titanate, beryl, pezzotaite, tourmaline, synthetic opal, lead glass, hydrozincite, dumortierite

This article reviews blue shortwave-excited luminescence (BSL) in natural and synthetic materials, focusing on seven minerals and gems—such as beryl (morganite), dumortierite, hydrozincite, pezzotaite, and elbaite—as well as three reference materials where BSL is linked to titanate groups (TiO₆): benitoite, Ti-doped synthetic sapphire, and spinel. Under 254 nm excitation, these materials exhibit broad blue emission centered at 420–480 nm, with excitation spectra peaking at 230–290 nm and luminescence decay times around 20 μs. The study proposes that this BSL is due to TiO₆ groups present at concentrations ≥20 ppmw, with no other known luminescence activators matching this behavior.

gems, corundum, treatments.6, ruby, sapphire, low-temperature heating, diaspore, goethite, Raman

Gem-quality rubies and sapphires are often commercially heat treated at about 800°C or higher to enhance their color and clarity, and hence quality. For this study, selected corundum samples containing diaspore and goethite inclusions were heated step-by-step to a maximum of 1000°C with the aim of monitoring the dehydration and phase transformation of these oxyhydroxides to corundum and hematite during heating. Based on our experiments and in agreement with the literature, the dehydration of diaspore in corundum occurs between 525 and 550°C, whereas goethite transforms to hematite between 300 and 325°C. As both diaspore and goethite may be present as inclusions in rubies, sapphires, and other corundum varieties (e.g., pink sapphires, padparadscha), these dehydration reactions and phase transformations can be considered important criteria to separate unheated from heated stones, specifically in cases in which other methods (e.g., microscopy, FTIR) are unsuccessful.

gems, corundum, History.1, Arab gemology, Arabic mineralogy, pearl, spinel, Indian lapidary

In The Genius of their Age, S. Frederick Starr follows up his acclaimed Lost Enlightenment: Central Asia's Golden Age with a portrait of the Arab enlightenment and its key figures--Abu-Ali al-Husayn ibn-'Abdallah Ibn-Sina and Abu al-Rayhan Muhammad ibn Ahmad al-Biruni. A thousand years ago, these two intellectual giants--known as Ibn Sina and Biruni for short--achieved stunning breakthroughs in fields as diverse as medicine, astronomy, mathematics, philosophy, geography, and physics. Biruni measured the earth more precisely than anyone else down to the sixteenth century, pondered a heliocentric universe, and hypothesized the existence of North and South America as inhabited continents. Ibn Sina's writing on philosophy and metaphysics enriched the writings of countless European thinkers, including St. Thomas Aquinas, while Sina's grand synthesis of medical knowledge became the standard for the next six hundred years in Europe, the Middle East, and India. They both also commented extensively on the works of ancient Greeks and earlier Muslim thinkers, whose works they aspired to synthesize--and to transcend. Contemporaries, Ibn Sina and Biruni were born within the borders of what is now Uzbekistan and spent their lives in Central Asia. They also became rivals, launching a correspondence and commentary that galvanized them despite sometimes bitter disagreement. Centuries before the West caught up with them, Ibn Sina and Biruni reflected their age's feats and its intellectual high point, persisting with their inquiries and their independence amid turmoil and rapid change. Though scholars have long dissected the works of Ibn Sina and Biruni, S. Frederick Starr focuses also on their lives and the times in which they lived. By contextualizing their work and by making the age palpable to the reader, S. Frederick Starr gives the achievements of Ibn Sina and Biruni a holistic and unforgettably human dimension.

gems, corundum, history.1, ancient lapidaries

In early modern Europe precious and semiprecious stones were valued not only for their beauty and rarity but also for their medical and magical properties. Lorenzo de’ Medici, Philip II of Spain, and Popes Leo X and Clement VII were all treated with expensive potions incorporating ground gems such as rubies, diamonds, and emeralds. Medical and magical/astrological lapidaries, texts describing the stones’ occult and medical qualities as well as their abilities to ward off demons and incantations, were essential resources for their use. First published in Venice in 1502, Camillo Leonardi’s Speculum Lapidum is an encyclopedic summary of all classical and medieval sources of lithotherapy. In describing the natural, manifest, and occult properties of precious and semiprecious stones as well as their graven images and applications, the Speculum Lapidum provides tremendous insight into the role that medical astrology and astral magic played in the life of an Italian court in the early modern period. Liliana Leopardi’s English translation, complete with critical apparatuses, gives unprecedented access to this key text within the magical lapidary genre. A vital addition to the existing canon of lapidaria in translation, Leopardi’s work will be of special importance for students and scholars of the history of magic, medicine, religion, and Renaissance humanism, and it will fascinate anyone interested in the occult properties of precious and semiprecious stones.

gems, corundum, spinel, history.1, carbuncle, garnet

This study traces the linguistic, literary, and gemmological history of the escarboucle or carbuncle over approximately three millennia. Beginning with the red stones odem and nophek in the biblical breastplate, it follows their translation and reinterpretation through the Greek anthrax, Latin carbunculus, and French escarboucle. Ancient and medieval lapidaries associated the carbuncle with a fiery brilliance supposedly capable of illuminating darkness, while legends placed the luminous stone in the heads of dragons, griffins, eagles, and the serpent-like vouivre. Accounts by Theophrastus, Pliny, Marbode, Albertus Magnus, Jean de Mandeville, Cardan, Cellini, de Boodt, and others demonstrate how the term came to encompass sardonyx, carnelian, garnet, ruby, and spinel, whose reflected light could be intensified by polishing, rounded forms, metal foils, and controlled illumination. The development of crystallography and chemical mineralogy during the late eighteenth and early nineteenth centuries finally separated these materials into distinct species. The article also examines the origins and evolution of such names as ruby, pyrope, almandine, rhodolite, Bohemian garnet, spinel, and zircon, presenting the carbuncle as a historical category founded upon the appearance of fiery red light rather than a single mineral species.

gems, corundum, inclusions.5, USA.12, Montana.12, Rock Creek, Missouri River, Dry Cottonwood Creek

Montana has produced large volumes of sapphire from secondary deposits for more than 150 years. While early production was mostly for industrial use as watch and instrument bearings, modern heat treatment technology has enabled the deposits to be worked profitably as gemstone mines, bringing more of this material to the gem and jewelry trade than ever before. Although pale blue and pale green sapphires make up the bulk of the production, fine Montana sapphire comes in nearly every hue, including yellow, orange, purple, and pink, along with very rare finds of ruby. Secondary Montana sapphire shares some similarities with those from Umba and Songea in Tanzania, but it is generally straightforward to separate them on the basis of inclusion scenes and trace element chemistry fingerprints.

gems, spinel, Afghanistan, Tajikistan, balas ruby, Kuh-i-Lal

The quote at the top is from Abu Rayhan al-Biruni (973–after 1050), taken from his The Book Most Comprehensive in Knowledge on Precious Stones. This book is a remarkable combination of scholarship, rumors and references to earlier authors, in addition to al-Biruni’s own experiences from his travels and scientific experiments. Al-Biruni’s description of the Kuh-i-Lal mines and their prominent placement in his book provide detailed insight into the geology, mines and operations that produced the magnificent rubies that have made these mines legendary. Timur’s Ruby, the Black Prince’s Ruby, the Samarian Ruby and Catherine the Great’s Ruby, and other magnificent stones in the British, Indian, Iranian, Russian, French and Turkish treasuries, all originate from here. It is believed that the term Balas ruby, which was extensively used in Europe from the Middle Ages up to near modern times, is derived from Badakhshan. Pardieu and Farkhodova (2019) address the historical importance of this locality in their article “Spinel from Tajikistan, The Gem That Made Famous the Word ‘Ruby’.” Following their reasoning, it was the spinel from Kuh-i-Lal, and not the corundum from Mogok, that made ruby a famous gemstone. It was not until the late 19th century that modern science found these mines (the Russian Pamir expedition in 1892–95). At that time, only small-scale mining took place. Serious scientific studies were later carried out by Soviet scientists, and papers on their history and geology were published (see Pardieu and Farkhodova, 2019, for a bibliography). Obviously, given the historical importance and potential value of the mine produce, combined with the geopolitical hotspot location, very little of this research was shared outside the USSR until after its breakup. One of the scientists who visited the mines was the Russian historian Mira Bubnova. She conducted archaeological investigations at the mines in the early 1970s. She found some evidence that the operations may have started as early as the 8th century, and she also confirmed that the most intensive exploitation of the mine took place from the 9th to the 12th centuries, meaning that al-Biruni’s text is a valuable contemporary account from the most prominent period of mining.

gems, Arabic mineralogy, al-Biruni, ruby, corundum, history.1

The history of vision aids was hitherto written almost entirely with material gathered only from the West, where there is an unmatched wealth of information. Dealing with the Islamic world, one is struck by how little is known about the origins and early uses of vision aids in the cultures of Islamic lands. This article is an attempt to close this gap by presenting and analysing a few texts produced between the 11th and 14th centuries, in the Eastern and Western parts of the Islamic world, with regard to the knowledge about the use of vision aids. The aim of this paper is (1) to show that, according to reliable Arabic sources that are gradually emerging, vision aids are indeed inscribed in a larger Arabic-Islamic tradition of knowledge and know-how; (2) to provide clear evidence for the use of such tools and present texts that help understand their cultural background; (3) to move the chronology of vision aids a little backward in time; (4) to help write the first chapters in a general history of visions aids in the cultures of Islamic lands; (5) to create an awareness for this subject and spark a critical debate in what looks like a new field of investigation.