Skip to main content

index mineral

index mineral A diagnostic mineral in a regional metamorphic terrain whose first appearance, going in the direction of increasing metamorphic grade through the metamorphic sequence, marks the outer limit of a metamorphic zone. A line marking the first appearance of an index mineral is termed an ‘isograd’, and represents a line of constant metamorphic grade. To indicate the regional distribution of metamorphic grade the first appearance of index minerals in rocks of pelitic composition (i.e. shales) are usually mapped out in the field, as this type of rock is extremely sensitive mineralogically to changes in metamorphic grade.

Cite this article
Pick a style below, and copy the text for your bibliography.

  • MLA
  • Chicago
  • APA

"index mineral." A Dictionary of Earth Sciences. . 19 Apr. 2019 <>.

"index mineral." A Dictionary of Earth Sciences. . (April 19, 2019).

"index mineral." A Dictionary of Earth Sciences. . Retrieved April 19, 2019 from

Learn more about citation styles

Citation styles gives you the ability to cite reference entries and articles according to common styles from the Modern Language Association (MLA), The Chicago Manual of Style, and the American Psychological Association (APA).

Within the “Cite this article” tool, pick a style to see how all available information looks when formatted according to that style. Then, copy and paste the text into your bibliography or works cited list.

Because each style has its own formatting nuances that evolve over time and not all information is available for every reference entry or article, cannot guarantee each citation it generates. Therefore, it’s best to use citations as a starting point before checking the style against your school or publication’s requirements and the most-recent information available at these sites:

Modern Language Association

The Chicago Manual of Style

American Psychological Association

  • Most online reference entries and articles do not have page numbers. Therefore, that information is unavailable for most content. However, the date of retrieval is often important. Refer to each style’s convention regarding the best way to format page numbers and retrieval dates.
  • In addition to the MLA, Chicago, and APA styles, your school, university, publication, or institution may have its own requirements for citations. Therefore, be sure to refer to those guidelines when editing your bibliography or works cited list.