Magnetite is an iron oxide mineral renowned for being the most magnetic naturally occurring mineral on Earth. This property gives rise to its naturally magnetized form known as lodestone. Acquiring magnetite, whether for collecting or professional use, requires understanding its distinct characteristics and typical sources. This guide covers how to identify the mineral and where you can get samples.
Identifying Magnetite by Physical Properties
Magnetite is typically black or grayish-black with a metallic to submetallic luster, appearing opaque even in thin fragments. Its strong attraction to a common magnet is the most reliable diagnostic feature, setting it apart from almost all other naturally occurring minerals. For positive identification, a streak test confirms the mineral, as magnetite always leaves a black streak when rubbed across an unglazed porcelain plate. Its Mohs hardness ranges from 5.5 to 6.5. Specimens also feel noticeably heavy for their size due to their high specific gravity, which is typically around 5.2 g/cm³.
Locating Natural Magnetite Deposits
Magnetite forms across igneous, metamorphic, and sedimentary rocks. It is a common accessory mineral, often dispersed in small grains within igneous rocks like basalt and gabbro. In metamorphic settings, it forms when iron-rich rocks undergo heat and pressure.
The most accessible natural source for collectors is often in sedimentary deposits known as “black sand” accumulations. These sands are found along beaches, riverbeds, and stream banks, where dense magnetite grains have been concentrated by water. A strong hand magnet can easily separate the magnetic grains from non-magnetic material.
Magnetite is a significant component of banded iron formations, which are ancient sedimentary rocks containing vast deposits. Notable sources include areas with historical mining operations, such as the Lake Superior region, parts of Australia, Sweden, and Russia. Examining crushed rock or weathered material from iron-rich areas with a magnet is a practical way to find small samples.
Commercial and Retail Sources for Purchase
Purchasing magnetite is the most direct method for those requiring pure samples, specific crystal forms, or bulk material. Mineral and rock shops, both physical and online, are excellent sources for acquiring raw specimens or well-formed crystals, often prized for their octahedral shapes. These retailers cater to hobbyists and collectors seeking specific pieces or historically significant lodestone varieties.
Educational supply companies and science hobby retailers frequently sell magnetite in smaller, packaged forms for classroom use, laboratory experiments, or magnetic demonstrations. For applications requiring high purity or large volumes, industrial chemical suppliers and specialized distributors are the appropriate source. Industrial-grade magnetite is commonly sold as a finely ground powder for use in various applications, including dense media separation in coal washing and as a pigment in paints and ceramics. When purchasing, it is beneficial to confirm the grade or purity of the magnetite, especially for scientific or industrial use.