Normative Mineralogy Especially for Shales, Slates, and Phyllites

*Hans Wolfgang Wagner*

## **Abstract**

First, an insight into normative mineralogy and the most important methods for calculating the standard or norm minerals, such as the CIPW norm, is given. This is followed by a more detailed explanation of "slatenorm" and "slatecalculation" for low and very low metamorphic rocks, such as phyllites, slates, and shales. They are particularly suitable for fine-grained rocks where the mineral content is difficult to determine. They enable the determination of a virtual mineral inventory from full chemical analysis, including the values of carbon dioxide (CO2), carbon (C), and sulfur (S). The determined norm or standard minerals include the minerals—feldspars, carbonates, micas, hydro-micas, chlorites, ore minerals, and quartz. The advantages of slatenorm and slatecalculation compared to other methods for calculating normal minerals of sedimentary rocks are discussed.

**Keywords:** slates, shales, phyllites, norm mineral calculation, CIPW, slatenorm, slatecalculation, micas, hydro-micas, illite, low- and very low-grade metamorphism

## **1. Introduction**

A norm or standard mineral inventory is a fictitious inventory that, in contrast to the modal and in fact mineral inventory, is calculated from the oxides of a chemical analysis of rock. Each oxide is then divided by its molecular weight. These molecular numbers are then the basis for further calculations (**Table 1**).

The results of the calculations are given as standard or norm minerals. They are given as abbreviations and mostly in small letters such as q (or qu) = quartz or mu = muscovite. The standard minerals each have a clearly defined chemical composition. This distinguishes them from some minerals in nature that have a more complex composition, such as pyroxenes, amphiboles, or chlorites. In these cases, simplifications or end links of a mixture series are used [1–3].

Usually, standard minerals are frequently occurring rock-forming minerals. Only in exceptional cases do you have to use minerals that occur only rarely or not at all in nature. The norm mineral inventory should come as close as possible to the actual, modal mineral inventory, which is not always possible [1–3].

The CIPW (Cross, Iddings, Pirsson, Washington) norm [4] is the most common method for magmatites. The Rittman norm for igneous rocks or the Niggli norm for igneous rocks and metamorphic rocks are less common.

*Mineralogy*


### **Table 1.**

*The full chemical analysis for standard mineral calculations.*

There are other methods for standard mineral calculations for sediments, such as SEDNORM [5], SEDMIN [6], PELNORM [7], and a linear program without a name (mainly for sandstones [8]).

The slatenorm and the slatecalculation norm are used for fine-grained sedimentary rocks and very low and low-grade metamorphic rocks, such as shales, slates, and phyllites [9]. As new methods, they are dealt with in great detail here.

## **2. CIPW norm**

The CIPW system is one of the best-known and best-elaborated chemical classifications of igneous rocks. It was developed as early as 1902. The CIPW system (CIPW norm) is based on a normative mineral inventory. This normative mineral inventory consists of a number of standard minerals (**Table 2**).

With them, groups of substances of chemical analysis are summarized and thus the quite complex chemistry of the igneous rocks is made clearer. As before, however, the CIPW standard plays a major role for the purpose of comparing the chemical properties.

The calculation of the CIPW standard is carried out according to a specified scheme. It can be found in a number of publications [3, 4]. Computer programs have also been developed since 1965 [10]. Several websites now offer online facilities for calculating CIPW [11, 12].

There are now numerous suggestions for improvement and additions to the CIPW standard. In particular, a standard method that is consistent with a rock classification as recommended by the International Union of Geological Sciences IUGS has proven to be necessary. There will be detailed step-by-step instructions for a standard igneous


### *Normative Mineralogy Especially for Shales, Slates, and Phyllites DOI: http://dx.doi.org/10.5772/intechopen.102346*

### **Table 2.**

*The standard minerals in the CIPW norm [1–3].*

norm (SIN) presented [13]. The review of the main computer programs for the classification of igneous rocks in the sense of the IUGS leads to the new program "Igneous Rock Classification System" (IgRoCS) [14].
