Clear Quartz will typically show some inclusions like lines, waves or cracks. Glass is either perfectly clear or may show some bubbles. Clear Quartz is harder than glass so you can test it by trying to cut a piece of glass (something like a glass bottle) with the crystal.

Shine the crystal with vinegar. Soak one end of a cotton swab in white vinegar and use it to rub down each faceted side of the crystal or clump. Follow each stroke from the wet swab with a stroke from the dry end to remove the excess liquid.

But there are many minerals which have slight additions of color-causing elements in some specimens that cause it to be a different color. For example, pure Quartz (SiO2), is colorless, whereas Amethyst, a purple variety of quartz, has its purple color caused by traces of the element iron.

Some minerals glow or fluoresce under ultraviolet (UV) light, such as some shown here. Apatite, quartz, orthoclase feldspar, and muscovite under normal white light and UV light.

Quartz belongs to the trigonal crystal class and accordingly is uniaxial. It is called uniaxial positive because ne > no. The optical axis in quartz corresponds to the c-axis of the unit cell, so there is no birefringence when light passes the crystal from tip to tip.

Negative uniaxial crystals (e.g. calcite CaCO3, ruby Al2O3) have ne < no so for these crystals, the extraordinary axis (optic axis) is the fast axis whereas for positive uniaxial crystals (e.g. quartz SiO2, sellaite (magnesium fluoride) MgF2, rutile TiO2), ne > n o and thus the extraordinary axis (optic axis) is the …

It is possible to tell whether a mineral is uniaxial positive or negative if the mineral has a characteristic elongate shape. Tourmaline, for example, is almost always elongate. This long dimension, in most cases, is the direction of the c-axis.

Transparent crystals of many species, including quartz, beryl. fluorite, topaz, tourmaline etc. etc. form ‘negative crystals’, though not always as attactively formed as in the excellent photos you show, Debbie.

What is the difference between a positive crystal and a negative crystal? Positive crystal : In this crystal velocity of O-ray is faster than E-ray and hence the refractive index of E-ray will be greater than O-ray (because n=c/v) where E-ray will be refracted closer to the optic axis than O-ray.

This crystal is described by one optical axis and two principal refractive indices. Examples of uniaxial Crystals are calcite, KDP, quartz, rutile etc. When light beam passes through such crystal, it splits into o-ray and e-ray >>.

The name quartz may be derived from querkluftertz, an old German word referring to whitish vein quartz. The name has also been said to derive from the ancient Greek word krustallos, meaning, ice, because the Greeks (and the Romans) believed that quartz was ice that never melted because it was formed by the gods.

Answer. Answer: What happens is that when unpolarized light enters the crystal from below, it is broken into two polarized rays that vibrate perpendicular to each other within the crystal. One ray, labeled o in the figure shown here, follows Snell’s Law, and is called the ordinary ray, or o-ray.

The Extinction Angle of Quartz is zero, which can be seen in the following graphics. In the first, quartz is fully visible, and the second has it completely extinct.

Quartz has a positive optical sign as can be seen by the increase of the retardation (blue color) observed in figure 1b along the high index of the wave plate (SW-NE orientation) or the black spots in the quarter wave plate image (figure 1c) appearing in a direction normal to the high index of the accessory plate.

In optical mineralogy, the irregular or wavy extinction seen in thin sections of mineral grains (e.g. quartz) on rotation of the stage. Different parts of the grain go into extinction in different orientations. The phenomenon is thought to result from strain, which may modify crystal orientation slightly.

In thin section, when viewed in plane polarized light (PPL), quartz is colorless with low relief and no cleavage. Its habit is either fairly equant or anhedral if it infills around other minerals as a cement.

Quartz varieties based on color centers are pleochroic, and their color centers can be destroyed by heat treatment. Note that individual quartz crystals may contain several colored varieties, like an amethyst with smoky zones.

symmetrical extinction In optical mineralogy, the phenomenon which occurs when the vibration direction of the light bisects the angles between two sets of cleavages (as seen in basal sections of pyroxenes and amphiboles).

Minerals can have a parallel extinction position, where the mineral is extinct when cleavage lines and the elongate direction of the mineral are parallel to the cross-hairs. The mineral is therefore extinct every 90 degrees on the cross-hairs, and at a maximum at 45 degrees to the cross-hairs.

EXTINCTION (X-POLARS)—Isotropic minerals and substances (like glass) are completely extinct under x polars. So when the mineral is oriented along the cross hairs, it will not go extinct. The angle between the orientation of the crystal and extinction is called the extinction angle.

Anisotropic minerals go extinct between crossed polars every 90° of rotation. Extinction occurs when one vibration direction of a mineral is parallel with the lower polarizer. The only change in the interference colours is that they get brighter or dimmer with rotation, the actual colours do not change.

Most common rock-forming minerals are anisotropic, including quartz and feldspar. Anisotropy in minerals is most reliably seen in their optical properties. An example of an isotropic mineral is garnet.