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The term 'Yellow Turquoise' is a commercial misnomer for a variety of minerals that are not true turquoise. Genuine turquoise is a hydrous phosphate of copper and aluminum, typically blue to green. The material sold as 'Yellow Turquoise' is most frequently a yellow-green to yellowish variety of Serpentine, Jasper, or Howlite, often with dark veining (matrix) that mimics the appearance of natural turquoise. It is important to note that true yellow turquoise is exceedingly rare and its yellow color would be due to specific trace elements, not a primary characteristic of the mineral itself. The vast majority of 'Yellow Turquoise' on the market is a different mineral entirely, often dyed or treated.
How to Identify
- Color
- Typically yellow-green to yellowish, often with dark brown, black, or grey matrix veining. The color is often uniform due to dyeing.
- Luster
- Waxy to dull, sometimes sub-vitreous. True turquoise has a waxy to sub-vitreous luster.
- Texture
- Smooth to slightly granular, often with a fine-grained appearance. The matrix can create a rougher texture.
- Crystal Form
- Massive, nodular, or botryoidal. Rarely forms distinct crystals. If it's Serpentine, it can be fibrous (chrysotile) or platy (antigorite, lizardite). If Howlite, it's typically nodular or massive.
- Cleavage
- None to poor. Serpentine can have one perfect cleavage (antigorite) or none (lizardite). Howlite has no cleavage.
- Geological Environment
- If true turquoise, it forms in arid regions as a secondary mineral in aluminum-rich igneous rocks that have been altered by phosphatic waters. If Serpentine, it forms from the hydrothermal alteration of ultramafic rocks. If Howlite, it forms in evaporite deposits.
Key Facts
- Hardness: Varies widely depending on the actual mineral: Serpentine (2.5-5), Howlite (3.5), Jasper (6.5-7). True turquoise (5-6).
- Specific Gravity: Varies widely: Serpentine (2.5-2.6), Howlite (2.53-2.59), Jasper (2.58-2.91). True turquoise (2.6-2.9).
- Crystal System: Varies: Serpentine (monoclinic), Howlite (monoclinic), Jasper (trigonal/hexagonal - cryptocrystalline). True turquoise (triclinic).
- Color: Yellow-green to yellowish, often with dark matrix.
- Luster: Waxy to dull, sometimes sub-vitreous.
- Transparency: Opaque.
- Fracture: Conchoidal to uneven.
- Cleavage: None to poor (Serpentine can have one perfect cleavage).
- Composition: Varies widely: Serpentine (magnesium iron silicate hydroxide), Howlite (calcium borosilicate hydroxide), Jasper (silicon dioxide). True turquoise (hydrous copper aluminum phosphate).
Quick Check
- Color: Yellow-green to yellowish, often with dark matrix.
- Luster: Waxy to dull.
- Streak: White (for Howlite or Serpentine), or colorless (for Jasper).
Physical Characteristics
- Crystal Habit: Massive, nodular, botryoidal. Rarely forms distinct crystals.
- Cleavage Type: None to poor. Serpentine can exhibit one perfect cleavage.
- Fracture Type: Conchoidal to uneven.
- Tenacity: Brittle.
- Luster Type: Waxy, dull, sub-vitreous.
Formation
The material marketed as 'Yellow Turquoise' is rarely true turquoise. It is most commonly a form of Serpentine, Jasper, or Howlite that has been dyed or stabilized to achieve a yellow-green to yellow color, often with a matrix resembling natural turquoise. True yellow turquoise (a rare variant of turquoise) would form in arid regions through the alteration of aluminum-rich igneous rocks by phosphatic waters, typically in secondary enrichment zones.
Usage
Primarily used in jewelry, ornamental carvings, and decorative items. Due to its often lower hardness and porous nature (if it's Howlite or Serpentine), it is frequently stabilized or dyed for durability and color enhancement.
Age Distribution
Varies depending on the actual mineral composition; typically associated with hydrothermal alteration in various geological ages.
Where to Find
China
A significant source of various minerals marketed as 'Yellow Turquoise', particularly Serpentine and Howlite.
United States (e.g., Arizona, Nevada)
While these states are known for true turquoise, genuine yellow turquoise is extremely rare. Most 'Yellow Turquoise' from these regions would be misidentified or treated material.
Africa (e.g., South Africa)
Sources of Serpentine that may be marketed as 'Yellow Turquoise'.
Finding Tips
Be Skeptical of the Name
The term 'Yellow Turquoise' is almost always a trade name for a different mineral. Assume it is not true turquoise unless proven otherwise by a reputable gemological laboratory.
Observe Color Uniformity
If the color is unnaturally uniform or vibrant, it may indicate dyeing. Natural turquoise (even rare yellow variants) would likely have more subtle color variations.
Check Hardness
True turquoise has a Mohs hardness of 5-6. Serpentine is 2.5-5, Jasper is 6.5-7, and Howlite is 3.5. A scratch test (on an inconspicuous area) can help differentiate, but be cautious not to damage the specimen.
Examine Matrix
While natural turquoise has matrix, examine if the matrix in 'Yellow Turquoise' appears painted on or unnaturally distinct, which can indicate treatment.
Similar Rocks
Serpentine
Mg3Si2O5(OH)4
Also known as: Antigorite, Lizardite, Chrysotile
Jasper
SiO2
Also known as: Chert, Chalcedony
Howlite
Ca2B5SiO9(OH)5
Also known as: White Turquoise (when dyed blue)
True Turquoise
CuAl6(PO4)4(OH)8·4H2O
Also known as: Turquoise
Scientific Classification
- Mineral Class
- Varies: Silicates (Serpentine, Jasper), Borates (Howlite), Phosphates (True Turquoise).
- Group
- Varies: Serpentine Group, Quartz Group, Borate Minerals, Phosphate Minerals.
- Crystal System
- Varies: Monoclinic (Serpentine, Howlite), Trigonal/Hexagonal (Jasper), Triclinic (True Turquoise).
- Chemical Formula
- Varies: Mg3Si2O5(OH)4 (Serpentine), Ca2B5SiO9(OH)5 (Howlite), SiO2 (Jasper), CuAl6(PO4)4(OH)8·4H2O (True Turquoise).
- Composition
- Varies widely depending on the actual mineral being sold as 'Yellow Turquoise'.
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