3.4: Mineral Properties: Visual Properties

Mineral Properties: Visual Properties

Properties can be organized into three major categories: visual, testable, and special or unique properties.

 Color

This represents the outward color of the mineral and reflects atomic bonding or trace impurities. The outward color may be light, dark or anywhere in between. The color could be solid or mottled, and may even show iridescence Links to an external site. (Figure 3.3).

An iridescent mineral called labradorite in a green igneous rock.

Figure 3.3: The mineral labradorite, which displays iridescence. (CC-BY 2.0, James St. John via Flickr Links to an external site.).

Clarity

­This represents the minerals’ ability to transmit light. If light is easily passed through, and the mineral is see-through, it is described as being transparent. If light cannot pass through a mineral it is described as being opaque. If a mineral can pass light through, but is unable to be see-through, it is described as translucent. Certain minerals may have unique optical properties, like double refraction or fiber optics.

Luster

Luster refers to the appearance of the reflection of light from a mineral’s surface. Typically, there are two major luster categories, metallic, and non-metallic. Minerals with a metallic luster Links to an external site. are typically opaque and appear as tarnished metal to a polished metal surface (Figure 3.4, left). A non- Links to an external site.metallic lust Links to an external site.er Links to an external site. encapsulates many possible appearances, from earthy to pearly, waxy to dull, glassy to silky (Figure 3.4, right). Submetallic lusters are also possible, and more subtle than a true metallic luster.

On the left, the metallic mineral gold, and on the right the non-metallic bubbly looking mineral nephrite jade.

Figure 3.4: Left: A gold nugget from California displaying a metallic luster. Right: Botryoidal nephrite jade from California displaying a non-metallic, waxy luster. (CC-BY 2.0, James St. John Left, Flickr Links to an external site.; Right, Flickr Links to an external site.).

Crystal Shape, Form or Habit

By definition all minerals are crystals, however some minerals will have a distinct crystal shape Links to an external site. (Figure 3.5). This shape is determined by the minerals’ growth space. If a mineral has time and space to develop it forms crystals faces. These faces intersect to form a distinct crystal shape. Perfect crystals are rare, and are often what we associate with minerals viewed in a museum. Should a mineral not have space to grow, then no distinct crystal shape will develop. A mineral with no distinct geometry is given the term massive or compact Links to an external site..

Mineral forms, from left to right and top to bottom, prismatic, bladed, twinned, radial, botryoidal, dendritic.

Figure 3.5: Various crystal habits and representative mineral examples. (CC-BY 4.0, Emily Haddad, own work).