Basalt
A species of Igneous, Also known as Lava Rock, Lavasteen Scientific name : Basalt RockType : Igneous
Basalt, A species of Igneous
Also known as:
Lava Rock, Lavasteen
Scientific name: Basalt
RockType: Igneous
Description
Basalt is a dark, iconic rock that forms when lava rapidly cools. Many famous geological structures, including the Giant's Causeway in the UK and the Devil’s Postpile in California, are made from basalt. Though relatively uniform in color and texture, the rock may take on many fascinating shapes, ranging from towering, perfectly angled hexagonal columns to billowy basalt pillows (formed when lava cools underwater).
Physical Properties
Colors
Dark grey to black
Texture
Aphanitic
Chemical Properties
Silica (SiO2) Content
45%-52%
People often ask
General Info
How to Select
When evaluating basalt, a type of volcanic rock, several characteristics can make certain varieties more desirable:
1.Texture: Fine-grained basalt, also known as 'aphanitic', is often preferred for ornamental uses due to its smooth texture and consistent coloring.
2.Mineral Content: basalt rich in olivine ('Olivine Basalt') or those with visible large crystals embedded in the matrix ('Porphyritic Basalt') are often sought after by collectors and researchers.
3.Vesicularity: Certain types of basalt, like "Vesicular Basalt", "Scoria", and "Amygdaloidal Basalt" have numerous cavities caused by gas bubbles. These are often desirable for their unique appearance and lightweight nature.
4.Columnar Structures: "Columnar Basalt" forms distinctive column-like structures upon cooling, which makes it appealing for landscaping and architectural purposes.
5.Color: Although color can range from black to gray, darker basalt is usually desired as they signify higher iron and magnesium content.
6.Hardness and Durability: Harder, denser basalt is typically more desirable for construction use due to its durability and resistance to weathering.
Remember that the desirability of basalt often depends on its intended use - whether for scientific study, construction, or aesthetic purposes.
Usage
Basalt is a popular choice in construction, and has been used in cobblestones and floor tiles because it is strong and a great thermal insulator. Additionally, it is used to construct roads as well as the ballasts for railroad tracks. Research is currently underway to utilize this rock in carbon sequestration in order to battle ongoing climate change.
Composition
By definition, basalt is an aphanitic (fine-grained) igneous rock with generally 45–53% silica (SiO2) and less than 10% feldspathoid by volume, and where at least 65% of the rock is feldspar in the form of plagioclase. This is as per definition of the International Union of Geological Sciences (IUGS) classification scheme. It is the most common volcanic rock type on Earth, being a key component of oceanic crust as well as the principal volcanic rock in many mid-oceanic islands, including Iceland, the Faroe Islands, Réunion and the islands of Hawaiʻi. 
Types
- Tholeiitic basalt is relatively rich in iron and poor in alkali metals and aluminium. Included in this category are most basalts of the ocean floor, most large oceanic islands, and continental flood basalts such as the Columbia River Plateau.
- High-alumina basalt may be silica-undersaturated or -oversaturated (see normative mineralogy). It has greater than 17% alumina (Al2O3) and is intermediate in composition between tholeiitic basalt and alkali basalt; the relatively alumina-rich composition is based on rocks without phenocrysts of plagioclase. These represent the low silica end of the calc-alkaline magma series.
- Alkali basalt is relatively rich in alkali metals. It is silica-undersaturated and may contain feldspathoids, alkali feldspar, phlogopite, and kaersutite. Augite in alkali basalts is titanium-enriched augite, and low-calcium pyroxenes are never present.
- Boninite is a high-magnesium form of basalt that is erupted generally in back-arc basins, distinguished by its low titanium content and trace-element composition.
- Ocean island basalts include both tholeiites and alkali basalts, with tholeiite predominating early in the eruptive history of the island. These basalts are characterized by elevated concentrations of incompatible elements. This suggests that their source mantle rock has produced little magma in the past (it is undepleted.)
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