Bentonite is a dark-grey to dark-green clay-rich rock composed of mostly montmorillonite, with minor concentrations of cristobalite, zeolite, and quartz, among others. Bentonite formation occurs when volcanic ash is altered by low-grade hydrothermal alteration. Alteration products of this type are distributed within Tertiary strata in Yamagata, Miyagi, Gunma, and Shimane Prefectures.

Bentonite is famous for having a very high swelling capacity, expanding around 80% when saturated with water. Both Na and Ca types exist and when wet, turn to viscous fluid and jelly, respectively. Na rich bentonite is used: as mud for drilling, in the production of casts, and in construction. Ca rich bentonite is used for cat litter-box sand, and fertilizer. Also, bentonite mixes well with oil and in this form is used in paints, wax, cosmetics, and medical supplies.

The Tono District, which spans from Aichi to Gifu Prefectures, is home to the Kibushi and Gaerome clays and boasts the most productive ceramic industry in all of Japan. Kibushi clay contains abundant wood particles, is dark brown in color, and composed of mostly kaolinite. Gaerome clay is a white, kaolinite based clay, which contains many sand size quartz frangments. It is said that they sparkle like frogfs (kaeru) eyes (me) and that is where the name Gaerome comes from. From the Miocene to Pliocene, where Ise Bay exists today, there was a lake called Tokai Lake and a portion of the sediments deposited in the vicinity of this lake consisted of weathered granite sand.

When either the Kibushi or Gaerome clays are mixed with water, the particles sort as they settle, separating the clay from the quartz sand and other sedimentary particles. The clay can then be used for ceramics and the quartz sand used to manufacture glass, casting material, and construction supplies.

Hydrothermal clays (above) contain abundant silica (SiO2) and alumina (Al2O3) and are soft and quite slippery, due to their fine grained nature. They are produced by hydrothermal alteration of silica rich volcanic rocks and contain minerals such as pyrophyllite, kaolinite, and other phyllosilicates, as well as, diaspore, corundum, andalusite, and alunite. Hydrothermal clays are found in abundance within Cretaceous volcanics in the Chugoku (central) region of Japan. Hydrothermal clays are used to produce glass fiber as well as refractory bricks, construction materials, ceramics, paper products, and as a carrier for agricultural chemicals.

The raw material mined for use in ceramics is called pottery stone. Pottery stone deposits form where rhyolitic lava or dikes are hydrothermally altered and contain, along with quartz and feldspars, sericite, kaolinite and other clay minerals. Pottery stone was first discovered in Japan in the early seventeenth century in the Arita area in Saga Prefecture. Since around that time Aritayaki has become a famous brand of ceramics and is known by collectors throughout the world. At present, the pottery stone for Aritayaki is called Amakusa Pottery Stone and is mined in Kumamoto Prefecture. Its plasticity and perfectly white color has given Amakusa Pottery Stone its reputation as the highest quality material for ceramics in Japan today. Pottery Stone can also be found in: Ishikawa, Gifu, Ehime, and Nagasaki Prefectures.

At present, pottery stone is not just used to make beautiful ceramics. It is also used to make tiles, high temperature insulation, in addition to other industrial applications, including manufacturing strong dish-wear for use in school cafeterias.

Near areas of active volcanism, depressurization of magma results in the production of steam and highly acidic primary magmatic fluid, both of which have the ability to alter lavas and tuffs of andesitic to rhyolitic compositions. The majority of the components are released into the fluid and the resulting rock becomes extremely silica rich. Silicastones formed by the process described above are found on Izu Peninsula in Shizuoka Prefecture.

Plagioclase phenocrysts dissolve easily and they leave vugs within the silicastone. This type of silicastone is easy to grind and is used not only to make glass but as a raw material in the production of many industrial and domestic products. One important product is aerated lightweight concrete (ALC), which is light, strong, and fire resistant and used in construction all over Asia and Australia. Due to the lightweight and heat resistant nature of glass fiber produced from silicastone, it is used widely in the manufacturing of sports equipment, insulation, and soundproofing. The chemical stability of powdered silica stone makes it an ideal carrier for agricultural chemicals.

When feldspars and quartz occur in large-scale concentrations, they can be effectively mined for industrial use. Pegmatitic concentrations of feldspars and quartz (above), which yield crystals multiple centimeters long, occur in granites as the product of late stage magmatic crystallization. Feldspars and quartz can also be concentrated through hydrothermal replacement or weathering of granites.

Feldspars are found in: the Shigaraki area of Shiga Prefecture (replacement feldspar); the town of Nagiso, Nagano Prefecture (weathered granite); the Kanamaru Mine, Niigata Prefecture (pegmatitic feldspar); among many other localities. They are used in the manufacturing of insulation, ceramics, and tiles as well as sanders, grinders and road paint.