What does porphyritic and porphyroid mean ?
Porphyritic : definition
This term designates magmatic rocks containing large crystals (porphyroblasts), dispersed in a microcrystalline paste (porphyritic rhyodacites for example, as in the photo opposite). We sometimes speak of "porphyry", this name is not very petrographic and obsolete, it concerns both acidic and basic volcanic rocks or even microgranites, it remains mainly used in the ornamental rock industry.
Porphyroid : definition
Please note, porphyritic should not be confused with "porphyroid", which qualifies magmatic rocks (mostly plutonic rocks) with large crystals scattered in a background of smaller crystals but clearly visible to the naked eye (granites porphyroids for example, as in the photo opposite).
