Mafic igneous rocks, like basalt, are dark colored and low in silica.
If it is also an igneous rock, it would be described as a mafic rock, like basalt. There are many other rocks, not necessarily igneous, that would also fit this description.
Granite is actually high in silica, which is why it is considered a felsic igneous rock. An example of an igneous rock low in silica is basalt, which is mafic in composition and contains less silica than granite.
Basalt is an igneous rock with low silica content that flows easily due to its low viscosity when molten. It often forms from volcanic eruptions and is found in oceanic crust and volcanic islands. Basalt is dark in color and fine-grained, with a composition of around 45-52% silica.
A light-colored rock that has high silica content is likely to be granite. Granite is a common igneous rock composed mainly of quartz, feldspar, and mica, and is known for its high silica content and light color.
Basalt is an igneous rock with low silica content that flows easily due to its fluid nature when erupted. It is commonly found in volcanic areas and is dark in color.
Mafic igneous rocks, like basalt, are dark colored and low in silica.
Mafic igneous rocks, like basalt, are dark colored and low in silica.
Generally, igneous rocks that are low in silica are dark relative to those that are high in silica. This tendency is largely the result of rocks low in silica having increased iron. Iron minerals tend to adsorb significant amounts of the visible spectrum and hence appear dark. I want to emphasize that this is a general tendency and there are exeptions -- obsidian which is very high in silica is typically a dark to black rock and a special igneous rock call carbonatite is very light in color but has little silica.
The igneous rock you are referring to is basalt. It is a fine-grained, dense, and dark-colored rock that forms from low-silica magma rich in iron and magnesium.
If it is also an igneous rock, it would be described as a mafic rock, like basalt. There are many other rocks, not necessarily igneous, that would also fit this description.
because an obsidian rock has low silica
Granite is a silicate because it contains 70-77% silica (SiO2). Granite is a rock, and silica is mineral containing the chemical elements silicon (Si) and oxygen (O). Si and O chemically combine to form SiO2. Rocks are made up of minerals, which are made up of chemical elements. Because silicon and oxygen are the two most common chemical elements in the Earth's crust, silicate rocks are very common.
They are not low in silicate minerals. They are still primarily composed of them. However, the amount of silica in them is lower than in the lighter-colored rocks. The lightest igneous rocks (felsic) are at least 70% silica while the dark ones (mafic) are between 45% and 52% silica. Silica content below 45% is deemed ultramafic.
Granite can exist in several colors. The colors are based on the ratio of feldspar, quartz, and mica.
The lower the viscosity is the hotter the magma is and faster it flows.Higher the viscosity is the cooler it is and slower it flows down.
Mafic magma is typically rich in magnesium and iron minerals, with a low silica content. It has a high temperature and low viscosity, allowing for it to flow easily. Mafic magmas commonly form basaltic rocks when they solidify.
Rock itself is solid and so does not have visocosity. However, the lava that forms basalt is low viscosity.