Phenocryst - phenocryst

Japanese: 斑晶 - はんしょう（英語表記）phenocryst

Phenocrysts are relatively large crystals found scattered in fine-grained or glassy groundmass in porphyritic igneous rocks. They are usually large enough to be seen with the naked eye [Iddings: 1889]. Phenocrysts are usually idiomorphic, but some become rounded when the surrounding area dissolves due to reaction with residual liquid, and some have reaction edges. The same type of mineral may be found in both phenocrysts and groundmass, but in these cases the shape and chemical composition of the minerals often differ between the phenocrysts and groundmass. The grain size of phenocrysts is not determined by absolute size, but is relative to the groundmass, and there are rocks that have both phenocrysts and groundmass that are coarse-grained. It basically refers to the difference in the conditions under which the two were formed. The Greek words phaino mean clear, and crystallus means crystal [Iddings: 1889]. Those that can be seen with the naked eye are sometimes called megaphenocrysts, while those that are too small to be seen without a microscope are called microphenocrysts [Cross, et al.: 1906].

Phenocrysts

In German, it refers to a large mineral found in the matrix of a rock. It is the equivalent of the English word porphyritic constituent [Hatch: 1888].

Source: Asakura Publishing Dictionary of Petrology Information

Japanese:

斑状の火成岩の中で，細粒またはガラス質の石基中に散在する比較的大きな結晶．普通は肉眼で認められる程度の粒度のもの［Iddings : 1889］．斑晶は普通は自形を呈するが，残液との反応によって周囲が溶解して丸味をおびるもの，反応縁を有するものなどがある．同一種類の鉱物が斑晶と石基の中に認められる場合があるが，この場合に斑晶と石基では鉱物の形状や化学成分が異なることも多い．斑晶の粒度は絶対的な大きさで決まるものではなく，石基に対する相対的なもので，斑晶，石基ともに粗粒の岩石も存在する．基本的には両者の形成条件の差を意味するものである．ギリシャ語のphainoは明らかな，crystallusは結晶の意味である［Iddings : 1889］．肉眼で識別できるものを巨斑晶（megaphenocryst），顕微鏡を用いないと識別できない小さなものを微斑晶（microphenocryst）と区別することがある［Cross, et al. : 1906］．