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Exceptional Quartz with Japan-law twins, 6 twins counted, from the 9 September Mine in Madan, Bulgaria. Specimen collected in 1997.
What is a twin? In mineralogy, a twin is the regular intergrowth of two crystals following a precise geometric rule. The Japan-law twin for quartz forms a flattened “V” with a characteristic angle of about 84.33°. Seen from the front, it is sometimes referred to as a “butterfly habit.”
The Madan district is a classic locality for polymetallic deposits (galena, sphalerite, pyrite), where cavities often host quartz druses (a druse is a surface covered with numerous small crystals). During the 1990s, the 9 September Mine produced several well-regarded lots of quartz, including Japan-law twins.
Anecdote: the term “Japan-law twin” comes from specimens described in the 19th century from Japanese localities; the name has remained for this quartz twinning law.
✅ Mineralogical Information
Name: Quartz (Japan-law twins)
- Chemical formula: SiO₂
- Color: Colorless to white, with contrasts due to the dark matrix
- Hardness (Mohs): 7
- Density: ~2.65 g/cm³
Quick definitions
– Matrix: the host rock that supports the crystals.
– Druse: a surface covered with many small crystals.
– Japan-law twin: the intergrowth of two quartz crystals forming a V at ~84.33°.
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