Goshenite
Chemical formula: Be₃Al₂(Si₆O₁₈)
Goshenite is a colorless, pure variety of beryl, valued in jewelry and by collectors for its high transparency and luster.
Properties
- Mohs hardness
- 7.5-8
- Luster
- Szklisty
- Streak
- Biała
- Density
- 2.6-2.8
- Cleavage
- Niewyraźna wg {0001}
- Fracture
- Muszlowy do nierównego
- Transparency
- Przezroczysty do przeświecającego
- Crystal system
- Heksagonalny
Diagnostic features
## Identification The key diagnostic features of goshenite are its hexagonal crystal shape, high hardness (scratches quartz), and complete lack of color. It has a vitreous luster and is usually fully transparent. Unlike topaz, it does not exhibit perfect cleavage. ## Distinguishing from Similar Minerals Goshenite is sometimes confused with several other colorless minerals: - **Rock crystal (quartz):** Quartz is slightly softer (hardness 7), has a lower refractive index, and a different crystal form (trigonal), often terminated by pyramids. - **Topaz:** Colorless topaz is harder (8), denser, and has perfect basal cleavage, which goshenite lacks. - **Danburite:** It has similar hardness but crystallizes in the orthorhombic system and is denser. - **Phenakite:** It is very similar in hardness and appearance but crystallizes in the trigonal system and is much rarer. ## Crystal Forms Goshenite most often forms elongated, prismatic hexagonal crystals, terminated by flat basal faces (pinacoids). It also occurs as granular aggregates or radiating clusters.
Geological environment
## Genesis Goshenite primarily forms in granitic pegmatites, often in their miarolitic cavities, as one of the last products of residual magma crystallization. It can also occur in some metamorphic rocks, such as mica schists, and in hydrothermal veins. ## Mineral Associations This mineral often co-occurs with quartz (especially smoky quartz), feldspars (albite, orthoclase), muscovite, lepidolite, spodumene, various tourmalines (elbaite, schorl), as well as columbite and tantalite. ## Localities Historically important is Goshen, Massachusetts, USA. Currently, the best quality collector's and jewelry specimens come from pegmatites in Brazil (especially Minas Gerais state), Pakistan (Gilgit-Baltistan), Afghanistan, China, Namibia, and Russia (Urals). In Poland, trace amounts of beryl (without precise variety identification) have been found in the granite pegmatites of the Karkonosze Mountains and Strzegom.
Rarity
Not very common
For collectors
## Quality Criteria For collectors, the most important criteria are ideal transparency (so-called "water clarity"), absence of inclusions and fractures, and excellent crystal habit. Sharp, undamaged, fully terminated hexagonal prisms are most highly valued. Large, colorless, and clear goshenite crystals are rare and sought after. Specimens on a rock matrix, especially in association with other pegmatitic minerals (e.g., tourmaline, smoky quartz), command higher prices. ## Popular Localities The most prized specimens by collectors come from Brazil and Pakistan, from where large, vitreous, and perfectly formed crystals are obtained. Historical specimens from Goshen, USA, also have high value, as do those from some regions of Russia and Afghanistan.
Care and storage
## Cleaning Goshenite is a hard and durable mineral that can be safely cleaned in warm soapy water using a soft brush. Ultrasonic and steam cleaners are generally safe for clean specimens without inclusions or fractures, but caution is advised. ## What to Avoid Avoid sudden temperature changes, which can cause internal fractures (thermal shock). Despite its high hardness, goshenite is brittle and can be damaged by strong impact. It should be protected from contact with harder materials, such as diamond or corundum, which can scratch it. ## Storage Goshenite specimens are best stored separately, in a soft pouch or a padded display box, to avoid scratching by harder stones and to prevent it from scratching softer minerals. It does not require special conditions regarding light or humidity.