Groundwater containing natural gas is referred to as natural gas brine, and this brine contains iodine, a globally valuable element.
Iodine, a halogen, is a semi-lustrous solid at room temperature. It sublimates readily, has a distinctive odor, and produces a purple vapor at room temperature.

▲ Iodine product

Atomic number	53
Element symbol	I
Atomic weight	126.9
Density	4.93ｇ／cm³ （20℃）
Melting point	113.6℃
Boiling point	184.4℃

Japan is the world's second largest producer of iodine after Chile. Of the iodine produced in Japan, 83% is produced in Chiba prefecture, 10% in Niigata prefecture, and 7% in Miyazaki prefecture.

Iodine is a highly valuable underground resource whose production in Japan is commercially significant worldwide.

Iodine, which has long been used as a raw material in pharmaceuticals, is currently used in a wide range of fields, from industrial applications to energy development. More recent applications include use in solar-powered hydrogen generation, which is drawing attention as a next-generation energy source, and use in coal liquefaction to produce an alternative to petroleum. Iodine is also used in advanced technological fields such as in drugs administered to protect the human body from radioactive contamination and as a material for generating laser beams. Iodine also has applications in daily living, such as in pharmaceuticals like X-ray contrast agents and new antibiotics; as an automobile seat belt and tire chemical fiber reinforcing agent; and as an agricultural chemical component and film media photosensitizing agent.