Aji Stone is a rare type of granite found exclusively in the northeastern part of Takamatsu City, Kagawa Prefecture, Japan. It is the only place in the world where this particular granite is quarried.
View of the stone mining site
Renowned for its exceptional hardness and refined beauty, Aji Stone ranks 7 on the Mohs hardness scale—equivalent to quartz. (For comparison, diamonds rank 10 and marble ranks 4.) Its fine grain and tightly bonded particles allow for detailed and precise craftsmanship. Due to its low moisture content, the stone is also highly resistant to weathering, making it remarkably durable.
Sometimes referred to as “blue granite” due to its bluish hue and the presence of biotite, Aji Stone has been highly valued since the Edo period (1603–1867).
Because of its hardness and density, advanced techniques are required to process it. Skilled artisans in the region specialize in the full range of processes involved—from quarrying, cutting, and polishing to shaping, engraving, and transportation.
However, the number of artisans working with Aji Stone is declining. We interviewed Mr. Chikara Ninomiya, President of Aoshima Co., Ltd., who launched the “AJI PROJECT” brand to reintroduce Aji Stone into daily life. His initiative aims to overcome competition from imported stones and address the lack of public awareness about Aji Stone’s unique appeal.
Mr. Ninomiya remarked, “The reason for the decline of the stone industry is that people without a background in stonemasonry took over the business.” Driven by efficiency and profit, these operators began importing inexpensive raw and processed stones from abroad, ultimately weakening the domestic production base.
One of Mr. Ninomiya’s first actions was to restore fair pricing. After decades of price competition and deflation, many craftsmen had lost sight of the true value of their work. Processing fees had remained unchanged for over 30 years.
When he took leadership of the company, Mr. Ninomiya also noticed a dramatic reduction in the number of stonemasons. A survey revealed that the number of companies had decreased from around 500 thirty years ago to just 200. While companies once employed up to 20 workers, many now operate with only one.
Although we typically see only the polished final product, Aji Stone is prone to natural flaws such as cracks. Only a small percentage of quarried stone is usable, and every step from extraction to finishing requires careful inspection and craftsmanship. These objects are more than functional—they are sculptural pieces shaped by human hands and guided by the strength and character of the stone itself.
Stone mining site
It takes at least four years of training to become a skilled Aji Stone artisan. Mr. Ninomiya hopes that if AJI PROJECT’s creations gain recognition both in Japan and internationally, more people will come to appreciate the beauty of Aji Stone—and some may even be inspired to become the next generation of stonemasons. With a material as rare and striking as Aji Stone, and the knowledge to shape it, that future may not be far away.
