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Cultured · Freshwater

Kasumiga pearls

Rare bead-nucleated freshwater pearls from Lake Kasumigaura, Japan, 60 km northeast of Tokyo. Typically 11 to 15 mm, known for rainbow iridescence, with output under 40 kg a year since 2013.

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Illustration of a typical kasumiga pearl. Move your pointer to turn the light.

At a glance

WaterFreshwater
MolluskHybrid of Hyriopsis schlegelii and Hyriopsis cumingii (developed 1962)
WhereLake Kasumigaura, Ibaraki Prefecture, Japan
Typical sizeTypically 11 to 15 mm; some over 16 mm
ShapesVaried
How it startsBead-nucleated (only nucleated culturing since 1991)
Growing timeAbout 3.5 to 4 years
0 mm5 mm10 mm15 mm20 mm

Typical size range from GIA. See sizes at actual size.

WhitePinkPurpleYellowOrangeBrown

Kasumiga pearls are bead-nucleated freshwater pearls from Lake Kasumigaura in Ibaraki Prefecture, Japan's second-largest lake, about 60 km northeast of Tokyo (GIA).

What makes them special

  • A hybrid mussel: a cross of Hyriopsis schlegelii and Hyriopsis cumingii, developed in 1962.
  • Size: typically 11 to 15 mm, with some over 16 mm.
  • Color: white, pink, purple, yellow, purple-red, orange and brown, often with iridescence. The "rainbow" effect is what they are known for, and pink and purple pearls command higher prices.
  • Long growth: about 3.5 to 4 years, building nacre about 3 mm thick over an 8 to 8.5 mm bead.
  • Scarcity: average output was 40 to 50 kg a year from 1991 to 2013, and less than 40 kg a year since.

All facts from GIA's 2018 study of Lake Kasumigaura cultured pearls.

History

Pioneering work on 10 mm nucleated pearls began in 1946. In 1962 about ten small farms moved to the lake and hybrid bead culturing succeeded. The lake switched entirely to nucleated culturing in 1991.

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Frequently asked questions

What are Kasumiga pearls?

Bead-nucleated freshwater pearls from Lake Kasumigaura, Japan, grown in a hybrid Hyriopsis mussel. Typically 11 to 15 mm, often iridescent, and produced in small amounts (GIA).

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Sources

Checked October 22, 2026. How we check our facts.