Aji stone is quarried from the rock cliffs of the mountains connected to Mt. Gokenzan (altitude 375m), which straddles the towns of Mure and Aji in Takamatsu City, Kagawa Prefecture. Aji stone, a type of granite, was formed around 100 million years ago as magma slowly cooled deep within the Earth. In other words, it can be said that Aji stone was born from the Earth’s depths. Initially formed at a depth of 5 to 10 kilometers underground, Aji stone is relatively light compared to other granites. Over the course of 20 million years, it was gradually pushed closer to the surface by other stones, eventually becoming the rocky mountain we can see today.

Aji stone is known for its fine grain, low water absorption rate, and toughness. Its toughness makes the stone resistant to chipping, allowing for intricate carvings, such as detailed facial features on statues. In the past, when large-scale transportation methods were not yet developed, stonemasons naturally gathered at the foot of Mt. Gokenzan, where Aji stone is quarried. This led to the area evolving into a production hub where everything from sourcing raw materials to processing could be done in one place. Today, specialized craftsmanship has developed, with different tasks divided among artisans—for example, cutting stone into rectangular blocks, extracting cylindrical shapes, or sculpting intricate forms. This specialization has increased the artisans’ expertise, allowing for the production of high-quality products while staying efficient.

Just like diamonds, there are a variety of styles of Aji Stone, each with its own particular feel and beauty. The main components found in Aji Stone are quartz, feldspar, and tiny bits of a dark brown mica known as biotite. According to the size of the grains of these, the stone is classified into different categories known as: komame and chume. Stone that is high in iron has an earthy brown tone and is known as sabi-ishi, or literally, “rusting stone.” This stone is known to easily grow moss, making it a popular choice for gardens.

Komame in particular, has many small grains of biotite within causing small specks call fu to appear on the surface. Fu is the visual ef fect in which a mottled pattern appears upon polishing the stone and creating a look described as, “if someone pressed their finger on the surface and moistened the stone.” This phenomenon is exclusive to Aji Stone and cannot be seen in any other stone material in the world. The unique presences this stone brings to any setting has been praised as the finest quality stone since some of the earliest days of Japan.