Megalithic Granite - Megalithic Granite

…A type of megacryst that develops into ball-shaped or lenticular crystals in association with plutonic rocks such as granite and porphyrite. It was once called megacryst granite because its mineral composition is often granitic. Volatile substances become abnormally concentrated in part of the residual magma that formed the parent plutonic rock, and as it gradually cools, it promotes the growth of minerals, resulting in the formation of pegmatite. …

*Some of the terminology explanations that refer to "megacrystalline granite" are listed below.

Source | Heibonsha World Encyclopedia 2nd Edition | Information

…花コウ岩，セン緑岩などの深成岩に伴われて，玉状，レンズ状に発達する巨晶岩。鉱物組成が花コウ岩質のことが多いために，かつては巨晶花コウ岩とも呼ばれた。母体である深成岩を形成したマグマの残漿の一部に揮発性物質が異常濃集し，徐々に冷却して鉱物の成長をうながし，ペグマタイトが生じる。…

※「巨晶花コウ岩」について言及している用語解説の一部を掲載しています。

出典｜株式会社平凡社世界大百科事典 第２版について | 情報