Is Tuff mafic or felsic

Answer 1

Pumice is more related to a textural feature, rather than a compositional attribute. For example, pumice originates when there are enough dissolved gases in the magma, such that when it is ejected from the volcano, the depressurization of the dissolved gases causes a rapid expansion as the gases exsolve (just like when you open a pop - the gases are initially under pressure, and you release that pressure by opening the can or bottle). The rapid change in temperature, from hundreds to thousands of degrees to the temperature of of the surrounding environment, causes a rapid cooling effect, whereby the expanding gases are frozen in place. These two factors are what give pumice its distinctive texture and ability to float when placed in water, as opposed to other volcanic rocks (such as scoria).

Whether or not the pumice is felsic (light in color) or mafic (dark in color) depends on its chemical composition and therefore, pumice can be both felsic or mafic depending on its parental magma.

General classification as to whether a rock is felsic or mafic is with regards to the silicate content of the rock as follows:

felsic < 69% SiO2

Intermediate Felsic 63 - 69% SiO2

Intermediate 52- 63% SiO2

Mafic < 52% SiO2

Ultra Mafic < SiO2

This said, felsic pumice (white or light tan brown colors) are more common to find than mafic pumice.

Answer 2

Tuff can be mafic, felsic, or intermediate, but it is more often felsic.

Answer 3

Neither. The terms mafic and felsic apply to igneous rocks. Limestone is a sedimentary/biochemical rock and so cannot be said to be mafic, felsic, or intermediate.

Answer 4

Mafic, felsic, and intermediate rocks can all have a porphyritic texture.