Silica Percentages of Igneous Rocks

Magma Composition and Igneous Rocks

Introduction In the following chapters we will find that nearly all of the varied aspects of volcanism are either directly or indirectly controlled by the chemical composition of magma and the rate at which it cools and solidifies. If you are to understand and appreciate subsequent discussions of volcanoes and related volcanic phenomena, it is essential that you have a good grasp of the basic c...

Occurrence, Texture, and Classification of Igneous Rocks

A paleointensity technique for multidomain igneous rocks

[1] We developed a paleointensity technique to account for concave-up Arai diagrams due to multidomain (MD) contributions to determine unbiased paleointensities for 24 trial samples from site GA-X in Pleistocene lavas from Floreana Island, Galapagos Archipelago. The main magnetization carrier is fine-grained low-titanium magnetite of variable grain size. We used a comprehensive back-zero-forth ...

AGeochemical Classification for Feldspathic Igneous Rocks

In this paper we classify the range of feldspathic igneous rocks using five geochemical variables: the FeO/(FeOþMgO) ratio or Fe-index, the modified alkali^lime index, the aluminum-saturation index, the alkalinity index, and the feldspathoid silica-saturation index.The Fe-index distinguishes between melts that have undergone extensive iron enrichment during differentiation from those that have ...

Thermal conductivity anisotropy of metasedimentary and igneous rocks

[1] Thermal conductivity anisotropy was determined for three sets of metasedimentary and igneous rocks from central Utah, USA. Most conductivity measurements were made in transient mode with a half-space, line source instrument oriented in two orthogonal directions on a flat face cut perpendicular to bedding. One orientation of the probe yields thermal conductivity parallel to bedding (kpar) di...