Lydite (Touchstone)
Quartz (Microcrystalline) var. Lydite · Mineral Specimen / Decorative Stone
Crystal System
Trigonal (Microcrystalline/Cryptocrystalline); typically found in massive or bedded forms without visible crystals.
Mineral Group
Silicates (Tectosilicate)
Chemical Formula
SiO2 with carbon and iron oxide inclusions
Formation Process
Sedimentary/Metamorphic; formed from the compaction of radiolarian oozes or fine-grained silica muds that have undergone low-grade metamorphism.
About This Crystal
A dense, fine-grained, velvet-black to dark grey variety of chert or jasper. It exhibits an opaque body with a dull to sub-vitreous luster and a smooth, almost velvety surface when fractured.
Physical Characteristics
Color: Black to charcoal grey with occasional reddish iron oxidation; Streak: White; Cleavage: None; Fracture: Conchoidal to splintery; Specific Gravity: 2.6-2.7; Tenacity: Brittle.
Optical Properties
Opaque; Refractive Index: approximately 1.54 (standard for chalcedony); Birefringence: None (isostructural mass); non-pleochroic; no distinct optical phenomena.
Hardness & Durability
Origin Region
Germany (Saxony), United Kingdom, and various locations worldwide; typically found in Palaeozoic sedimentary sequences.
Hardness & Durability
Mohs hardness: 6.5 to 7; High durability and resistance to most acids, making it suitable for testing precious metals.
Care & Maintenance
Wash with warm soapy water; very stable under sunlight and chemicals; avoid sharp impacts which could cause conchyoidal chipping.
Rarity & Value
Common; primarily valued for industrial or archaeological purposes rather than as a gemstone. Low monetary price range.
Special Characteristics
Historically used as a 'touchstone' to determine the purity of gold and silver by observing the color of the streak left on the stone's surface.
Lore & History
Used since antiquity (ancient Greece and Rome) as a tool for assaying metals. In metaphysical traditions, it is sometimes associated with grounding and the root chakra, though its primary significance remains historical and utilitarian.