While the previous minerals we’ve discussed have been neon-yellow or deep-sea blue, Abukumalite brings us into the realm of the “Earth Tones”—a mineral that looks like the soil but holds the secrets of rare-earth elements.
If you look for “Abukumalite” in a modern textbook, you might find it listed under a different name: Britholite-(Y). However, the story of its discovery in the mountains of Japan remains a classic piece of mineralogical history.
What is Abukumalite?
Abukumalite is a rare-earth silicate mineral belonging to the Apatite supergroup. It was first discovered in 1938 in the Suishoyama pegmatite, located in the Abukuma Range of the Fukushima Prefecture, Japan.
In 1966, mineralogists decided to standardize the names of rare-earth minerals. Because Abukumalite was chemically similar to Britholite but dominated by the element Yttrium, it was officially renamed Britholite-(Y). Despite the name change, seasoned collectors still use the old name to honor its Japanese heritage.
Quick Facts:
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Chemical Formula: $(Y, Ca)_5(SiO_4, PO_4)_3(OH, F)$
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Color: Reddish-brown, dark brown, or black.
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Hardness: 5 on the Mohs scale (similar to a pocket knife blade).
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Luster: Resinous to greasy (it can look a bit like hardened tree sap).
The “Metamict” State: A Mineral in Chaos
One of the most scientifically fascinating things about Abukumalite is that it is often metamict.
Because Abukumalite frequently contains trace amounts of radioactive elements like Thorium or Uranium, it undergoes a process called “self-irradiation.” Over millions of years, the radiation emitted from within the crystal actually breaks down its own internal structure.
The result? The mineral looks like a crystal on the outside, but on the inside, the atoms are in a state of chaotic disorder, more like glass than a structured crystal.
Where Does it Come From?
Abukumalite is typically found in granite pegmatites—massive, slow-cooled volcanic rocks that allow rare and “exotic” elements to concentrate into large crystals.
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Japan (Type Locality): The Abukuma massif remains the most famous source, specifically the Suishoyama pegmatite.
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Norway: Found in the high-alkaline rocks of the Drag area.
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Russia: Notable specimens have been found in the Kola Peninsula, a “Mecca” for rare-earth mineral hunters.
Why Is It Important?
Abukumalite isn’t just a curiosity for the shelf. It is a vital source of Yttrium and other Rare Earth Elements (REEs).
Yttrium is a “tech-metal” used in:
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LEDs and Phosphors: Creating the red color in older television screens and modern LED bulbs.
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Superconductors: Vital for high-tech energy and transport research.
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Camera Lenses: Adding yttrium oxide to glass makes it heat-resistant and shock-resistant.
Safety and Identification
Like many rare-earth minerals from pegmatites, Abukumalite can be mildly radioactive. While it’s not as “hot” as pure uranium minerals, it’s best to keep it in a display case rather than carrying it in your pocket.
Visually, it can be hard to distinguish from other brown minerals like Allanite. The key is often its association—if you find a resinous brown mineral in a pegmatite known for yttrium, you might just be looking at Abukumalite.
The “A-Group” Mineral Summary
| Mineral | Color | Key Element | Claim to Fame |
| Abernathyite | Yellow | Uranium | Neon fluorescence |
| Abriachanite | Blue | Iron | The “Blue Earth” of Loch Ness |
| Abukumalite | Brown | Yttrium | The tech-metal workhorse |