Augite is a common, dark-colored, rock-forming mineral found worldwide, belonging to the pyroxene group of silicates. It is widespread in various rock types but is not typically mined as a primary commodity. Augite’s uses are tied to its presence as a major component within broadly utilized rocks or to its specific value in scientific analysis. This allows augite to play an indirect role in large-scale industry and a direct role in geological research.
Augite’s Identity and Geological Context
Augite is chemically a complex silicate of calcium, magnesium, and iron, with the generalized formula \((\text{Ca},\text{Na})(\text{Mg},\text{Fe},\text{Al})(\text{Si},\text{Al})_2\text{O}_6\). This composition allows for significant variation due to elemental substitution. The mineral crystallizes in the monoclinic system, forming short, prismatic crystals. It exhibits two distinct cleavage planes intersecting at approximately \(87^\circ\) and \(93^\circ\), a characteristic feature of the pyroxene group.
Augite is a major constituent of mafic igneous rocks, such as basalt and gabbro, formed from the cooling of magnesium and iron-rich magma. It is responsible for the dark coloration of these rocks, typically appearing dark green, brown, or black. Augite possesses a Mohs hardness ranging from 5.5 to 6 and a high specific gravity (3.2 to 3.6). Because of its common occurrence, augite’s commercial utility stems from its physical presence within these abundant source rocks.
Bulk Industrial Applications
Augite is rarely extracted and processed alone, but its properties are leveraged when it is part of crushed mafic rock like basalt or gabbro. These rocks, which contain a significant percentage of augite, are quarried extensively for use in the construction industry. Augite’s hardness and high specific gravity contribute to the overall durability and density of the resulting crushed rock aggregate.
Crushed rock containing augite is widely used as a coarse aggregate in concrete mixes and asphalt pavement. The dense nature of augite-rich basalt makes it effective in road base material and as railway ballast. This material provides resistance to wear and the ability to bear heavy loads. Its incorporation can lead to concrete with increased compressive strength and high abrasion resistance, qualities partially attributable to the hard augite minerals.
Specialized industrial applications utilize the mineral’s chemical components. Augite’s composition, rich in calcium, magnesium, and iron, makes it a suitable raw material for synthesizing augite-based glass-ceramics and opaque glazes for ceramic tiles. These engineered ceramic products are valued for their high hardness and superior opacity. Furthermore, the mineral has been investigated for use as an abrasive material in grinding wheels and sandpaper, owing to its Mohs hardness.
Significance in Scientific Study
Augite holds importance in geological research, serving as a tool for understanding the formation of igneous and metamorphic rocks. Its ability to incorporate and exsolve other pyroxene components, like pigeonite, is sensitive to changes in temperature and pressure during crystallization. Scientists analyze the chemical zoning and microscopic intergrowths, known as exsolution lamellae, within augite crystals. This analysis helps reconstruct the temperature and pressure history of the magma chamber or rock formation process.
The calcium content in augite is useful for geothermometry, allowing researchers to estimate the temperatures at which magma cooled. Augite is also found in extraterrestrial samples, including lunar basalts and stony meteorites, underscoring its role in planetary science. Analysis of augite in these materials provides insights into the mineral composition and magmatic evolution of other celestial bodies.