Got a photo? Identify rocks instantly with the Rockby app
Open the appDescription
Heliodor is a variety of the mineral beryl, characterized by its yellow, golden-yellow, or greenish-yellow color. The name 'Heliodor' comes from the Greek words 'helios' (sun) and 'doron' (gift), meaning 'gift of the sun'. It shares the same chemical composition and crystal structure as other beryl varieties like emerald (green), aquamarine (blue-green), and morganite (pink). Its color is stable under normal conditions but can be altered by heat treatment or irradiation in some cases.
How to Identify
- Color
- Yellow, golden-yellow, greenish-yellow. The color is typically uniform but can show slight zoning.
- Luster
- Vitreous (glassy).
- Texture
- Smooth to slightly uneven on fracture surfaces.
- Crystal Form
- Typically forms hexagonal prisms, often with striations parallel to the c-axis. Terminations can be flat basal pinacoids or pyramidal faces.
- Cleavage
- Imperfect basal cleavage {0001}, often not observed in fractured specimens.
- Geological Environment
- Granitic pegmatites, hydrothermal veins, and greisens associated with granitic intrusions. Often found alongside quartz, feldspar, muscovite, and other pegmatite minerals.
Key Facts
- Hardness: 7.5-8 on Mohs scale
- Specific Gravity: 2.65-2.80 g/cm³
- Crystal System: Hexagonal
- Color: Yellow, golden-yellow, greenish-yellow
- Luster: Vitreous
- Transparency: Transparent to translucent
- Fracture: Conchoidal to uneven
- Cleavage: Imperfect basal {0001}
- Composition: Beryllium aluminum cyclosilicate (Be3Al2Si6O18)
Quick Check
- Color: Yellow to greenish-yellow
- Luster: Vitreous
- Streak: White
Physical Characteristics
- Crystal Habit: Prismatic, typically hexagonal prisms, often striated parallel to the c-axis. Can also be massive or granular.
- Cleavage Type: Imperfect basal {0001}. Often not observed in hand specimens or fractured material.
- Fracture Type: Conchoidal to uneven. This is the more common breakage pattern.
- Tenacity: Brittle
- Luster Type: Vitreous (glassy)
Formation
Heliodor forms primarily in granitic pegmatites, which are coarse-grained igneous rocks that crystallize from residual magma enriched in volatile components and incompatible elements like beryllium. It can also be found in some hydrothermal veins and greisens associated with granitic intrusions. The yellow to greenish-yellow color is attributed to trace amounts of Fe3+ (ferric iron) substituting for Al in the beryl crystal structure. Irradiation, either natural or artificial, can enhance or induce the yellow color in some beryls.
Usage
Heliodor is primarily used as a gemstone in jewelry due to its attractive color, good hardness, and transparency. It is cut into various facets, cabochons, and sometimes carved. It is also a collector's mineral.
Age Distribution
Heliodor, like other beryls, forms in geological environments that can range from Precambrian to Cenozoic, depending on the specific pegmatite or hydrothermal deposit. Its formation is not tied to a specific geological age but rather to the conditions conducive to beryl crystallization.
Where to Find
Brazil
Minas Gerais is a significant source, particularly for large, high-quality crystals.
Namibia
Known for producing fine golden-yellow heliodor crystals.
Ukraine
Volyn region is a historical source of large heliodor crystals.
Madagascar
Produces heliodor, often with a greenish-yellow hue.
Russia
Ural Mountains and other regions have yielded heliodor.
United States
Localities in Connecticut, Maine, and North Carolina have produced beryl, including some heliodor.
Finding Tips
Geological Context
Focus on areas known for granitic pegmatites. Look for outcrops of coarse-grained igneous rocks, especially those with large crystals of quartz, feldspar, and mica.
Associated Minerals
Heliodor is often found with other pegmatite minerals such as quartz, feldspar (orthoclase, albite), muscovite, biotite, tourmaline, and sometimes garnet or topaz.
Crystal Habit
Look for hexagonal prismatic crystals. While cleavage is imperfect, the characteristic crystal shape can be a strong indicator.
Color and Luster
Identify the characteristic yellow to greenish-yellow color and vitreous luster. In the field, this can help distinguish it from other minerals.
Hardness Test
If possible and appropriate, a scratch test (Mohs hardness 7.5-8) can help differentiate it from softer minerals like citrine (Mohs 7) or harder ones like sapphire (Mohs 9).
Similar Rocks
Citrine
Quartz (variety Citrine)
Also known as: Lemon Quartz, Madeira Citrine
Yellow Sapphire
Corundum (variety Sapphire)
Also known as: Pukhraj
Chrysoberyl
Chrysoberyl
Also known as: Cat's Eye, Alexandrite
Topaz
Topaz
Also known as: Imperial Topaz, Sherry Topaz
Scientific Classification
- Mineral Class
- Silicates
- Group
- Cyclosilicates (Beryl Group)
- Crystal System
- Hexagonal
- Chemical Formula
- Be3Al2Si6O18
- Composition
- Beryllium aluminum cyclosilicate. The yellow color is due to trace amounts of Fe3+ (ferric iron) substituting for Al in the crystal lattice.
Explore Heliodor
Identify rocks anywhere
Free on iOS, Android, and Web. Photo identification, full database, and your personal collection.