The brightness is the physical property that describes the aspect of the surface of mineral when when light is reflected on it. The brightness of a mineral is totally independent of the color of said mineral.
For example, the brightness of a mineral can be:
- Metallic: if its shine is similar to that of metals, such as galena.
- Vitreous: if the brightness is similar to that of glass, such as quartz. This shine is the most common among minerals.
- Pearly: if it looks like pearls. For example, mica.
- Greasy: if it resembles a greasy surface, such as talcum powder.
- Adamantine: its brilliance is similar to that of diamond.
- Matte: if its appearance is dull and dull.
The transparency is the property that some minerals to let light pass through them.
Minerals, as they allow the passage of light, can be classified as:
- Transparent mineral: allows light to pass through and allows the shape of an object behind it to be clearly appreciated , such as some calcite or halite crystals .
- Translucent mineral: allows light to pass through but the shapes of the object behind it are not clearly appreciated, such as aragonite or fluorite.
- Opaque mineral: totally prevents light from passing through them, such as pyrite or magnetite.
Although at first glance, most of the minerals appear opaque, if a microscopic cut is made it can be seen that they are translucent minerals. This allows the use of the microscope to be one of the most reliable ways to identify minerals, since their recognition of visu is very complicated.
The color of a mineral depends on the light that the mineral reflects. It is one of the most striking and easy to observe characteristics, and it can be decisive to identify a mineral such as azurite (blue), olivine (olive green), sulfur (yellow), malachite (green), ..., but you have to keep in mind that, in some cases, any impurity in the mineral can cause it to change its color. There are also minerals, such as fluorite, which can have different shades, such as blue, green, purple, pink, etc.
Therefore, although it is probably the first thing we look at when we see a mineral, we have to exercise some caution when using it to determine what mineral it is.
This property is useful to identify the mineral in situ if we have a white porcelain in which to make the line and be able to observe its color, since the color of the line is constant for each mineral, unlike the color that can vary from one exemplary to another.
The luminescence is the property that some minerals emit light after absorbing some form of energy.
For example, some minerals, such as fluorite, emit light when illuminated with ultraviolet light.
When the luminescence ceases after the energy form has ended, we speak of fluorescence. On the other hand, if it remains after having finished that form of energy, it speaks of phosphorescence.
The birefringence or double refraction is an optical property of having some minerals, such as Iceland spar (a variety of calcite), consisting of unfolding an incident beam of light into two, forming a double image.
As a curiosity, it is worth highlighting the "television effect" of ulexite, in which the text below it is projected onto its surface, leaving the surface as a kind of television.
- Properties that depend on light, in Geology of the 2nd year of Baccalaureate.
- Shine of a mineral, in Geology of 2º of Baccalaureate.
- Transparency of a mineral, in Geology of 2º of Baccalaureate.
- Color of a mineral, in Geology of 2º of Baccalaureate.
- Stripe of a mineral, in Geology of 2º of Baccalaureate.
- Luminescence of a mineral, in Geology of 2º of Baccalaureate.
- Propiedades ópticas de los minerales, de Biología y Geología 1º ESO.
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