Synthetic chrysoberyl – HDSM
Introduction to Chrysoberyl
The mineral or gemstone chrysoberyl is an aluminate of beryllium with the chemical formula BeAl2O4. Chrysoberyl is often celebrated for its unique features, resilience, and aesthetic appeal. It is a gemstone that has fascinated people for centuries due to its distinct characteristics, such as its remarkable hardness and mesmerizing varieties. Chrysoberyl is notable for being the third-hardest natural gemstone commonly encountered, with a hardness of 8.5 on the Mohs scale, making it a durable option for jewelry.
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Origin and Properties of Chrysoberyl
The name “chrysoberyl” originates from the Greek words “chrysos,” meaning “gold,” and “beryllos,” which refers to a gemstone. This translates to “a golden white spar.” Despite the similarities in their names, chrysoberyl and beryl are entirely different minerals. The only commonality between them is that they both contain beryllium.
Varieties of Chrysoberyl
Ordinary chrysoberyl is typically yellowish-green, ranging from transparent to translucent. When the mineral exhibits a vibrant green to yellow color and maintains transparency, it is classified as gemstone-quality chrysoberyl. The primary varieties of chrysoberyl include ordinary yellow-to-green chrysoberyl, cat’s eye (cymophane), and the famous color-changing alexandrite. Each of these varieties offers a distinct visual appeal that has captivated collectors and gemstone enthusiasts.
Historical Context
Historically, yellow-green chrysoberyl was often called “chrysolite,” particularly during the Victorian and Edwardian eras. However, this terminology led to confusion since “chrysolite” was also used to describe the mineral peridot. Consequently, this term is no longer used in gemological circles to describe chrysoberyl.
Bagdasarov Modification (HDSM)
Introduction to the HDSM Technique
Synthetic chrysoberyl, specifically grown using the “Horizontal Directional Solidification Method” (HDSM), was an innovation introduced by Kh.S. Bagdasarov in 1964. This groundbreaking technique marked a major step forward in single-crystal growth technology. Bagdasarov’s method involves moving a crucible containing raw material and a single crystal seed in a horizontal direction, a process that has proven effective not only for laser crystals but also for gemstone production.
Application of the HDSM Method
The HDSM method was initially developed for growing large, highly perfect Nd-doped yttrium-aluminum garnet laser crystals. The technique demonstrated significant success in producing large and visually flawless synthetic gemstones, including synthetic chrysoberyl. These crystals are distinguished by their uniformity, clarity, and exceptionally smooth surfaces, characteristics that were previously challenging to achieve with other methods.
Growth Process of Synthetic Chrysoberyl
The growth process of synthetic chrysoberyl through the HDSM method can be described as follows:
- A seed crystal, oriented in a specific crystallographic direction, is placed at the front tip of the container. The container, which resembles a horizontal ship, holds the raw material for the crystal growth.
- The container is positioned in a specialized furnace designed to maintain precise temperature control throughout the growth process.
- The entire growth process is carried out in either a vacuum or an inert gas atmosphere to ensure the purity of the crystals.
- A camera is positioned above the furnace to monitor and diagnose the growth process, providing continuous supervision to maintain high-quality standards.
- Once the desired crystal growth is complete, the melt is slowly cooled to promote optimal crystallization and avoid structural stress.
Advantages of the HDSM Method
The HDSM method allows for the production of large slabs with almost perfect edges in any given crystallographic orientation, such as the C-plane, M-plane, R-plane, or A-plane. These slabs are suitable for a wide range of optical, mechanical, RF, and LED applications due to their superior optical quality and structural integrity.
Unique Features of the HDSM Technique
One of the unique aspects of the HDSM technique is the ability to conduct repeated crystallization, which is useful when additional chemical purification of the raw material is required. Moreover, it is possible to carry out continuous crystallization by gradually moving the crucible through the crystallization zone, allowing for the uninterrupted production of high-quality crystals.
Temperature Control and Quality
The HDSM method is also noted for its precise temperature control, which is crucial for growing large-size single crystals with minimal defects. This control enables the formation of synthetic chrysoberyl with characteristics that closely resemble natural gemstones, yet with enhanced consistency and optical properties.
Applications and Benefits of Synthetic Chrysoberyl
Synthetic chrysoberyl crystals produced by Bagdasarov’s method are well-regarded for their excellent optical properties, making them suitable for demanding applications in various industries. The flawless nature of these crystals, combined with their high refractive index and absence of inclusions, makes them ideal for use in jewelry and advanced optical technologies.
Specifications of Synthetic Chrysoberyl – HDSM
Synthetic Chrysoberyl – HDSM
- Chemical Formula: BeAl2O4:Cr3+
- Crystal System: Rhombic
- Hardness (Mohs): 8.5
- Density: 3.7 g/cm3
- Refractive Index: 1.741 – 1.75
- Dispersion: 0.015
- Inclusions: Inclusions free. Key separations from natural chrysoberyl include fogs, cracks, holes, multi-phase inclusions, quartz, biotite, and fluorite.
Growing Market for Synthetic Chrysoberyl
The use of synthetic chrysoberyl in the gemstone market has increased in recent years, particularly due to its high-quality visual properties that rival those of natural stones. The ability to produce synthetic chrysoberyl with specific orientations and enhanced purity makes it an attractive choice for both gemstone collectors and manufacturers of optical devices.
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