pollucite

Japanese: pollucite

...The following minerals are called rare element minerals. They are minerals of rare alkali elements in group IA on the periodic table, i.e., lithium, rubidium, and cesium, such as lepidolite K(Li,Al) ₃ (Si,Al) ₄ O ₁₀ (F,OH) ₂ and pollucite (Cs,Na) ₂ Al ₂ Si ₄ O ₁₂ ･H ₂ O. In group IIA, they are minerals of beryllium, such as beryl Be ₃ Al ₂ Si ₆ O ₁₈ .

From [Cesium]

…It occurs widely in small amounts in association with other alkali metal elements. A known cesium mineral is pollucite Cs _{1－ x} Na _x AlSi ₂ O _6. It occurs in small amounts in association with the lithium mineral lepidolite and the potassium mineral carnallite. …

*Some of the terminology that mentions "pollucite" is listed below.

Source | Heibonsha World Encyclopedia 2nd Edition | Information

Japanese:

…以下の鉱物などが希元素鉱物と呼ばれている。元素の周期表上でIA族の希アルカリ元素すなわちリチウム，ルビジウム，セシウムの鉱物でリシア雲母lepidolite K(Li,Al)₃(Si,Al)₄O₁₀(F,OH)₂，ポルクス石pollucite (Cs,Na)₂Al₂Si₄O₁₂･H₂O等。IIA族ではベリリウムの鉱物で緑柱石Be₃Al₂Si₆O₁₈等。…