Got a photo? Identify rocks instantly with the Rockby app
Open the appDescription
The term 'Yellow Gemstone' without further identification refers to any gem-quality material exhibiting a yellow hue. This broad category encompasses several distinct minerals and synthetic materials, most commonly Citrine (a variety of quartz), Yellow Sapphire (a variety of corundum), and yellow-colored Cubic Zirconia. Each possesses unique physical and chemical properties, making precise identification crucial for accurate geological and commercial assessment. The yellow color in these materials can arise from different chromophores: iron impurities in citrine, iron and/or color centers in yellow sapphire, and specific dopants (e.g., cerium) in cubic zirconia.
How to Identify
- Color
- Ranges from pale yellow to golden yellow, orange-yellow, or brownish-yellow. Hue, saturation, and tone are important for differentiation.
- Luster
- Vitreous (glassy) for all three, though sapphire can exhibit a sub-adamantine luster due to its high refractive index.
- Texture
- Smooth to conchoidal fracture surfaces when broken. Crystal faces, if present, are typically smooth.
- Crystal Form
- Citrine: Hexagonal prisms with pyramidal terminations. Yellow Sapphire: Hexagonal dipyramids, tabular, or prismatic. Cubic Zirconia: Typically faceted into various gem cuts, rarely found as raw crystals outside of laboratory settings, but would be isometric.
- Cleavage
- Citrine: None. Yellow Sapphire: No true cleavage, but exhibits parting along basal planes and rhombohedral planes. Cubic Zirconia: None.
- Geological Environment
- Citrine: Hydrothermal veins, pegmatites, and alluvial deposits. Yellow Sapphire: Metamorphic rocks (e.g., marble, gneiss), igneous rocks (e.g., basalt), and secondary alluvial deposits. Cubic Zirconia: Exclusively synthetic, formed in controlled laboratory environments.
Key Facts
- Hardness: Citrine: 7; Cubic Zirconia: 8-8.5; Yellow Sapphire: 9 (Mohs scale)
- Specific Gravity: Citrine: 2.65; Yellow Sapphire: 4.00; Cubic Zirconia: 5.6-6.0
- Crystal System: Citrine: Trigonal; Yellow Sapphire: Trigonal; Cubic Zirconia: Isometric
- Color: Pale yellow to golden yellow, orange-yellow, brownish-yellow
- Luster: Vitreous (glassy) to sub-adamantine
- Transparency: Transparent to translucent
- Fracture: Conchoidal
- Cleavage: Citrine: None; Yellow Sapphire: No true cleavage, but parting; Cubic Zirconia: None
- Composition: Citrine: Silicon dioxide (SiO2); Yellow Sapphire: Aluminum oxide (Al2O3); Cubic Zirconia: Zirconium dioxide (ZrO2)
Quick Check
- Color: Yellow to orange-yellow
- Luster: Vitreous to sub-adamantine
- Streak: White (for all three)
Physical Characteristics
- Crystal Habit: Citrine: Prismatic, often terminated. Yellow Sapphire: Tabular, prismatic, bipyramidal. Cubic Zirconia: Typically faceted, rarely as raw isometric crystals.
- Cleavage Type: Citrine: Absent. Yellow Sapphire: Parting on {0001} and {1011}. Cubic Zirconia: Absent.
- Fracture Type: Conchoidal
- Tenacity: Brittle
- Luster Type: Vitreous to sub-adamantine
Formation
Varies significantly depending on the specific gemstone. Citrine forms in igneous and metamorphic rocks, often from hydrothermal alteration of amethyst. Yellow Sapphire forms in metamorphic rocks or as primary crystallization in igneous rocks. Cubic Zirconia is synthesized in laboratories.
Usage
Primarily used in jewelry as a decorative gemstone. Also used in some industrial applications (e.g., sapphire in optics, zirconia in ceramics).
Age Distribution
Geological ages vary widely for natural minerals; synthetic materials are modern.
Where to Find
Brazil
Major source of natural citrine, particularly from the state of Rio Grande do Sul. Also a source of amethyst which is often heat-treated to produce citrine.
Sri Lanka (Ceylon)
Historically and currently a significant source of high-quality yellow sapphire, often found in alluvial deposits.
Madagascar
Produces various colors of sapphire, including yellow, from both primary and secondary deposits.
Australia
Known for its sapphire deposits, including some yellow varieties, particularly in Queensland and New South Wales.
Africa (various countries)
Several African nations, including Tanzania and Kenya, produce yellow sapphire. Namibia and Zambia are known for citrine.
Laboratories Worldwide
Cubic Zirconia is produced globally in industrial laboratories using various growth methods (e.g., skull melting).
Finding Tips
Hardness Test
A scratch test can differentiate between these materials. Citrine (Mohs 7) will scratch glass but not sapphire. Yellow Sapphire (Mohs 9) will scratch citrine and glass. Cubic Zirconia (Mohs 8-8.5) will scratch citrine but not sapphire, and will scratch glass.
Refractive Index (RI) and Specific Gravity (SG)
These are definitive tests for gemologists. Citrine: RI ~1.54-1.55, SG ~2.65. Yellow Sapphire: RI ~1.76-1.77, SG ~4.00. Cubic Zirconia: RI ~2.15-2.18, SG ~5.6-6.0. These differences are significant and measurable with standard gemological equipment.
Inclusions and Growth Patterns
Natural gemstones often contain characteristic inclusions (e.g., two-phase inclusions in citrine, rutile needles in sapphire). Cubic Zirconia is typically flawless or may show gas bubbles or curved growth lines under magnification.
Pleochroism
Yellow Sapphire is dichroic (shows different colors when viewed from different angles), while citrine and cubic zirconia are not (or very weakly in citrine). This can be observed with a dichroscope.
Fluorescence
Some yellow sapphires may fluoresce orange or yellow under UV light, while citrine typically does not. Cubic Zirconia can show various reactions depending on dopants.
Similar Rocks
Citrine
SiO2
Also known as: Yellow Quartz
Yellow Sapphire
Al2O3
Also known as: Pukhraj
Cubic Zirconia (Yellow)
ZrO2
Also known as: CZ
Yellow Topaz
Al2SiO4(F,OH)2
Also known as: Imperial Topaz (golden-yellow to orange-yellow)
Yellow Beryl (Heliodor)
Be3Al2Si6O18
Also known as: Golden Beryl
Scientific Classification
- Mineral Class
- Citrine: Tectosilicate; Yellow Sapphire: Oxide; Cubic Zirconia: Oxide (synthetic)
- Group
- Citrine: Quartz group; Yellow Sapphire: Corundum group; Cubic Zirconia: Zirconia group (synthetic)
- Crystal System
- Citrine: Trigonal; Yellow Sapphire: Trigonal; Cubic Zirconia: Isometric
- Chemical Formula
- Citrine: SiO2; Yellow Sapphire: Al2O3; Cubic Zirconia: ZrO2
- Composition
- Citrine: Silicon dioxide with Fe3+ impurities. Yellow Sapphire: Aluminum oxide with Fe2+/Fe3+ impurities and/or color centers. Cubic Zirconia: Zirconium dioxide, often stabilized with Y2O3 or CaO, and doped with Ce for yellow color.
Explore Yellow Gemstone
Identify rocks anywhere
Free on iOS, Android, and Web. Photo identification, full database, and your personal collection.