?What is basalt

Many of you have most probably heard the name “basalt” through your academic career or on construction sites. You may have had questions about its type, characteristics and uses in construction and other industries. Basalt is one of the most common rock types on earth’s surface and thus used extensively in different industries such as construction. Due to this extensive use, we aim to familiarize you with this rock by going over its characteristics.

Basalt

If you wonder what type of stone basalt is, it should be mentioned that it is an extrusive volcanic igneous rock in the first place, meaning that it is formed from the cooling of lava, extruded onto the earth’s surface. Due to a low silica content (less than 52%), basalt is considered an alkaline rock. Low silica content results in low viscosity in molten basalt. Its lava, therefore, can spread over about 20 kilometers of surface area prior to cooling

Basalt is a flat, black, fine-grained volcanic rock which is the second most common igneous rock on earth’s surface after granite. Basalt is formed from volcanic deposits and therefore is found abundantly in Iran and other parts of the earth. Basalt is, interestingly, one of the most common rock types in other planets of the solar system.  For instance, vast areas (more than 80%) of the plains of Venus are covered in basalt. It is also the most common rock on the surface of Mars. Basalt is also abundant on the surface of the Moon. This is due to basaltic magma flowing under the surface of .the Moon. These dark, basalt covered areas of the Moon are called lunar maria

Types of Basalt                                                                                 

One of the most common rocks on earth’s surface after granite, this rock has different types. Some types, like tachylite , are volcanic glass and many are fine-grained, aphanite in texture

 Basalt is often porphyritic in texture, containing larger crystals (phenocrysts) of olivine, augite, or feldspars embedded in a crystalline matrix (groundmass). Olivine and augite are the most common porphyritic minerals in basalt. Other than olivine and augite, porphyritic plagioclase feldspars are also found in basalt. Basaltic lava is often vesticular in nature. Vesicles, formed by escaping gas and lava vapors, are filled with secondary minerals such as calcites, chlorites, and zeolites.

According to chemical and petrographic properties, basalt is generally categorized into two types: Tholeiitic basalt and alkali basalt.

The main mafic minerals of tholeiitic basaltic lava are calcic plagioclase, augite, pigeonite, hypersthene and olivine. Types without olivine also well exist. Tholeiitic basalt with a silica content of 45% to 63% is rich in iron and includes thulite (basalt with low-calcium pyroxene). This type is abundant in volcanic deposits of mountain belts.

Alkali basalt is relatively rich in alkali metals. It is silica-undersaturated and may contain feldspathoids, alkali feldspar, phlogopite, and kaersutite. Augite in alkali basalt is titanium-enriched, and low-calcium pyroxenes are never present. In some cases, basalt is classified into high and low titanium basalt, according to its titanium content.

Plagioclase feldspar and pyroxene content determines basalt’s mineral characteristics. Olivine can also be a determining constituent. Accessory minerals present in relatively minor amounts include iron oxides and iron-titanium oxides, such as magnetite, ulvöspinel, and ilmenite. Due the presence of such oxide minerals, basalt can acquire strong magnetic characteristics as it cools. In tholeiitic basalt, pyroxene (augite and orthopyroxene or pigeonite) and calcium-rich plagioclase are common phenocryst minerals. Olivine may also be a phenocryst.

Alkali basalts commonly have mineral assemblages that lack orthopyroxene but contain olivine. Feldspar phenocrysts are typically labradorite to andesine in composition. In contrast to tholeiitic basalt, augite in alkali basalt is rich in titanium. Basalt has high liquidus and solidus temperatures. With the liquidus temperature being 1200 °C or above, and the solidus temperature being 1000 °C or below; these values are higher than those of other common igneous rocks. The majority of tholeiitic basalts are formed at an approximately 50–100 km depth within the mantle. Many alkali basalts may form at greater depths, perhaps 150–200 km deep. Experts continues to have disagreements on the origin of high-alumina basalt, over whether it is a primary basaltic lava cooled into rock, or derived from other basalt types by fractionation.

Carbon dioxide absorption is another property of basalt. Laboratory and field research on the basalt structure of the Columbia River of North America revealed that carbon dioxide injected into basalt combines with its minerals to form carbonate compounds such as ankerite, preventing the release of carbon dioxide (a greenhouse gas) into the atmosphere.

Uses of Basalt

One of basalt’s most important applications is in the production of basalt fibers. Basalt is a neutral rock of the extrusive igneous type and is a natural substance. It is one of the most common rocks in the earth’s crust. Material with basaltic constituents are completely non-toxic and environmentally friendly. For these reasons, basalt is used in the production of basalt fibers.

One of the properties of basalt fibers, compared to glass fibers, is their high chemical stability, especially in highly acidic environments. These fibers are nonflammable and resistant to high temperatures. Due to their relatively high thermal resistance , basalt fibers have a thermal insulation three times better than that of asbestos. Due to this great thermal insulation, they are used for fire protection in watercraft. Research on fibers used in shipbuilding revealed that basalt fibers have comparable or better physical properties compared to E-glass fibers and thus are favorable for use in watercraft production.

These excellent protective characteristics of basalt fibers have made them a suitable, cost-effective alternative to glass fibers in shipbuilding, in the manufacturing of inexpensive, safe vessels for the transportation of personnel. Other applications of basalt fibers include:

• Alkaline environments cause no physical or chemical changes in basalt fibers. However, it is important to note that rock and stone building material and cement cause changes in the fibers, creating weak points at contact between cement and building material.
• Compressive strength in pure cement will increase by the addition of basalt fibers. This increase has a direct relationship with the length of basalt fibers, with longer basalt fibers further increasing the compressive strength. This increase is due to a homogenous environment in cement mortar, created by basalt fibers.
• Flexural strength in concrete will increase by the addition of basalt fibers 12mm in length, which are smaller than the largest aggregates in concrete. These fibers act as a binding agent for the aggregate which reduces damage. Basalt fiber-reinforced concrete has a 20% higher flexural strength than types without basalt fibers.

Basalt is used in its processed form and due to its variety in color, is favorable for use as road base, paver, and building veneer. Other basalt applications include its use as raw material in the production of composite plates, carbon dioxide absorption plates, brake pads, gas cylinders, building profiles, utility poles, automobile bodywork, and sports equipment.

Basalt is one of the common rocks on earth. It is formed from the cooling of lava and is thus the second most common rock on earth’s surface after granite. Its abundance and chemical and physical properties have resulted in its widespread use in different industries. Construction, shipbuilding and the automobile industry, sports equipment industries, and composite plate manufacturing are among the industries that utilize basalt in their production.