An Introduction to Several Common Raw Materials Used in Manufactured Sand and Gravel Production and

The main raw materials for manufactured sand and gravel include more than a dozen types, including granite, basalt, tuff, limestone, gneiss, and sandstone. These rocks can be categorized by their geological origin into three main categories: igneous rocks, sedimentary rocks, and metamorphic rocks. Below, we will examine typical examples and provide a detailed introduction to their characteristics and applications.

Representative igneous rocks: granite and basalt

Granite

Granite is an intrusive rock within the igneous rock family, often with colors ranging from light reddish-brown to light gray or off-white. Its primary mineral composition is quartz, potassium feldspar, and plagioclase, while minor minerals include biotite, hornblende, and sometimes a small amount of pyroxene. The quartz content is generally between 20% and 50%, with some rocks reaching 50% to 60%. Its Mohs hardness is 6 to 7, and its compressive strength ranges from 120 to 200 MPa.

Granite is the primary raw material for the production of manufactured sand and gravel. The resulting manufactured sand and gravel features fine particle shape, well-graded gradation, low crushing value, and minimal stone dust, making it suitable for high-strength concrete and projects requiring high durability. However, considerations should be given to the mica content, degree of weathering, and wear resistance of the crushing equipment.

Basalt

Basalt is a basic extrusive rock. Formed by volcanic magma that solidifies after cooling on the surface, it has a dense or foamy structure. It contains numerous dark minerals and is often dark gray or black. The main chemical components of basalt are silicon dioxide, aluminum oxide, iron oxide, calcium oxide, and magnesium oxide, with silicon dioxide accounting for approximately 45-52%. Its Mohs hardness is 5-7, and its compressive strength is generally above 140 MPa.

Basalt is a *-quality raw material for high-strength, highly wear-resistant manufactured sand and gravel. It is a * source of material for major projects such as hydropower projects, airport runways, highways, and railways. However, it faces challenges with high energy consumption and high wear. Therefore, a multi-stage crushing process (jaw crusher + single-cylinder cone crusher + multi-cylinder cone crusher) is recommended to reduce costs.

Representative sedimentary rocks: limestone and sandstone

Limestone

Limestone, formed by chemical or biological sedimentation, is a carbonate rock primarily composed of calcite. It sometimes contains dolomite, clay minerals, and detrital minerals. It comes in a variety of colors, including gray, off-white, gray-black, yellow, light red, and brown-red.

Limestone generally has a Mohs hardness of 3-4 and a compressive strength of 60-120 MPa. It has moderate crushability and abrasiveness. It is the primary raw material for manufactured sand and gravel aggregate production, accounting for over 30% of the industry's total. Due to its inherent structure and hardness, the crushed particles have poor shape. A jaw crusher + impact crusher is typically used to optimize and improve the particle shape. This method is suitable for ordinary concrete and construction mortar.

Sandstone

Sandstone is a sedimentary rock primarily composed of cemented sand particles with a diameter of 0.05-2 mm. The sand content must be *er than 50%. It has a stable structure and is typically light brown or red in color. Based on its primary composition, it can be divided into siliceous sandstone, ferruginous sandstone, calcareous sandstone, and argillaceous sandstone.

Limestone generally has a Mohs hardness of 3-4 and a compressive strength of 30-150 MPa, depending primarily on the quartz content and cementation type. Sandstones of different compositions and hardness require different processing equipment, resulting in different applications for the finished sand and gravel aggregate.

Representative metamorphic rocks: Gneiss and Quartzite

Gneiss

Gneiss is formed by deep metamorphism of igneous or sedimentary rocks. It features a gneissic structure characterized by alternating dark and light-colored minerals arranged in directional or banded patterns, exhibiting a metamorphic structure. The main minerals are quartz, feldspar, hornblende, and mica.

Gneiss has a Mohs hardness of 5-7, making it a cost-effective source of manufactured sand. It can be configured with a jaw crusher + cone crusher + vertical shaft impact crusher (sand making machine) to improve crushing efficiency and refine the sand and gravel grain size.

Quartzite

Quartzite is a metamorphic rock primarily composed of quartz (quartz content *er than 85%). It is formed by metamorphism of quartz sandstone and siliceous rock. It generally has a massive structure, a granular metamorphic structure, and is a crystalline aggregate. Quartzite comes in a variety of colors, including green, gray, yellow, brown, orange-red, white, blue, purple, and red.