Modal mineral inventory

The modal mineral composition of a rock is the relative ratio of the minerals occurring in it . It is usually given in percent by volume (% by volume), more rarely in percent by weight (% by weight). The modal mineral inventory is a descriptive petrographic parameter of a rock and is determined by microscopic counting of thin sections of rock with the help of a point counter . An assessment can also be made by looking at a handpiece with the help of a hand-held magnifying glass in the field, whereby the examination should be carried out on a fresh fracture point without the effects of weathering . In contrast to the normative mineral inventory , the modal mineral inventory is a real property of a rock and relates to the minerals actually occurring in it.

For many types of rock, especially for coarse-grained igneous rocks , but also for numerous rocks of metamorphic and sedimentary origin, the modal mineral inventory is an important criterion for the classification of e.g. B. in the route iron diagram .

literature

• JD Winter: An introduction to igneous and metamorphic petrology. Prentice Hall, Upper Saddle River, New Jersey, 2002. ISBN 0-13-240342-0