Properties of Common Minerals

Mining Visuals
May 2
2 min read

Minerals are the fundamental building blocks of rocks, forming the foundation of our planet and providing essential resources. From the humble Graphite in a pencil to sparkling Garnets in jewelry, minerals vary widely. But how do we tell these natural treasures apart? Geologists and enthusiasts rely on observing distinct physical properties, unique fingerprints that help identify each mineral species.

One of the most noticeable properties is Luster, describing how a mineral's surface reflects light. Is it shiny like a metal? Minerals like Pyrite ("Fool's Gold") and Galena exhibit a Metallic Luster. Or does it lack that metallic sheen? These are classified as Nonmetallic Luster, which can further be described as glassy (like Quartz), pearly (like Talc or Mica), earthy/dull, or waxy.

Next, we consider Hardness, a mineral's resistance to scratching. This is famously measured using the Mohs Hardness Scale, ranging from 1 (Talc, easily scratched by a fingernail) to 10 (Diamond, the hardest). The chart shows Quartz at a hardness of 7, meaning it can scratch glass, while Calcite, at 3, cannot. Testing hardness helps significantly narrow down possibilities.

How a mineral breaks is also diagnostic. Cleavage is the tendency to break along specific, flat planes due to weaknesses in the mineral's atomic structure. Mica peels into thin sheets, Halite breaks into cubes, and Calcite rhombuses – all examples of cleavage. If a mineral breaks irregularly, without smooth planes, it exhibits Fracture. Quartz, for instance, often shows a curved, shell-like 'conchoidal' fracture.

While Color seems like an obvious identifier, it can often be misleading as impurities can create a wide range of colors within the same mineral type (think of the many colors of Fluorite or Quartz). However, for some minerals like yellow Sulfur or grey Graphite, color is a key characteristic. Other properties like Streak (the color of the mineral's powder), crystal form, and density also play crucial roles in making a definitive identification.

Identifying minerals is like solving a puzzle. By carefully observing and testing these various physical properties – Luster, Hardness, Cleavage, Fracture, Color, and more – we can unlock the identity of these fascinating natural substances that tell the story of our Earth.

Source: Source: Physical Setting/Earth Science Reference Tables – 2010 Edition