spotted slate

geology

Written by

The Information Architects of Encyclopaedia Britannica

Last updated

July 14, 2026

Quick Summary

"Spotted slate" refers to a type of slate that exhibits a spotted appearance. This spotting occurs as the intensity of metamorphism increases, leading to the growth of porphyroblasts within the slate. As metamorphism progresses further, the average crystal size increases, and mineral segregation develops, potentially transforming the rock into phyllite.1

True slate is a fine-grained, clayey metamorphic rock formed under low-temperature and low-pressure conditions. It is characterized by its ability to split into thin, durable slabs along planes of cleavage, which are distinct from the original sedimentary bedding. Slates can display various colors, including black, blue, purple, red, and green, depending on the presence of minerals like carbonaceous material, iron sulfide, hematite, or chlorite.2

Summary created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

2 Britannica Sources

Ask Britannica AI about this topic

Britannica doesn't have a full article on this topic, so we've curated a list of our relevant coverage.

metamorphic rock
Slate
…such slates are sometimes called spotted slates. As metamorphism proceeds, the average crystal size increases, and mineral segregation develops; the rock then may be termed a phyllite.
Read More
…such slates are sometimes called spotted slates. As metamorphism proceeds, the average crystal size increases, and mineral segregation develops; the rock then may be termed a phyllite.
Read More