Quartz is one of the most common minerals on Earth. It is found in many different colors, including clear, white, gray, yellow, pink, purple, orange, red, brown, and black. The color of a quartz crystal is determined by impurities in the crystal structure. Iron impurities, in particular, can give quartz a brownish or reddish hue. Brown quartz goes by several different names depending on the exact shade and other properties. In this article, we will examine the different types of brown quartz and explain how they get their distinctive colors.
Varieties of Brown Quartz
Here are some of the most common varieties of brown quartz:
Smoky Quartz
Smoky quartz is one of the most well-known brown varieties of quartz. It ranges in color from light tan to deep reddish-brown. The brown color comes from natural radiation exposure over long periods of time. This radiation knocks loose aluminum atoms in the crystal structure, which then interact with other impurities to produce the smoky brown hue. Smoky quartz is found worldwide, especially in granite pegmatites.
Cairngorm
Cairngorm is a variety of smoky quartz found specifically in the Cairngorm Mountains of Scotland. It typically has a rich golden brown or whiskey color. The brown coloration comes from iron impurities in the crystal. Cairngorm has been popular in Scottish jewelry and ornamental carvings for centuries.
Morion
Morion is an old term used to refer to smoky quartz crystals that are very dark brown to black in color. The dark brown hue is so intense that morion can appear almost black. High concentrations of iron impurities and aluminum atoms produce this dark coloration. Morion is often found in silver ore deposits.
Citrine
While citrine is more well known for its yellow hues, some citrine crystals display an orange-brown color. Natural citrine’s color is caused by heat-treated iron impurities. The shade of citrine depends on the level of heat exposure and concentration of iron. Lower heat and iron content creates yellow citrine, while higher levels produce deep orange-brown hues. Most commercial citrine today is heat-treated amethyst, however.
Tiger’s Eye
Tiger’s eye is a fibrous variety of quartz known for its rich golden brown color with a silky luster. Tiger’s eye forms when quartz replaces crocidolite asbestos in a process called pseudomorphism. The asbestos fibers produce the chatoyant effect, or cat’s eye optical phenomena in gemstones. The iron content of the crocidolite gives tiger’s eye its characteristic golden brown color.
Hawk’s Eye
Hawk’s eye is a variety of tiger’s eye that contains more bluish asbestos fibers. This results in a gray-blue to bluish-gray color with brownish chatoyancy. The blue fibers temper the warm golden brown hues of regular tiger’s eye. Hawk’s eye is not as common as the yellowish form of tiger’s eye.
Brown Amethyst
While most amethyst is purple, some rare specimens can occur with red-brown hues. This is sometimes referred to as brown amethyst. The color is caused by iron impurities exposed to natural radiation from the earth. Unlike citrine, brown amethyst maintains its quartz structure and is not heat-treated. This makes genuine brown amethyst very rare and valuable. Most brown amethyst in jewelry has been altered from regular purple amethyst.
Rutilated Quartz
Rutilated quartz is transparent rock crystal quartz with golden needle-like rutile crystals passing through it. The rutile crystals are rich in iron and titanium oxides which give them a reddish-brown color. The rutile inclusions passing through clear or smoky quartz can create beautiful patterns and optical effects.
Where Brown Quartz is Found
Brown quartz can be found on every continent around the world. Some key deposit locations include:
| Country | Brown Quartz Locations |
| USA | Arkansas, California, Colorado, Georgia, Idaho, Montana, New Hampshire, North Carolina, South Dakota |
| Brazil | Minas Gerais |
| South Africa | Northern Cape Province |
| Namibia | Erongo Region |
| Madagascar | Tuléar Province |
| Scotland | Cairngorm Mountains |
| Switzerland | Valais Canton |
| Spain | Galicia, Catalonia |
| Austria | Carinthia, Tyrol |
| Australia | Western Australia, Queensland |
Brown quartz is commonly found in granite pegmatites, silver deposits, schist formations, and sedimentary conglomerates. Certain regions are famous for their specific types of brown quartz, such as cairngorm deposits in Scotland.
Uses of Brown Quartz
Thanks to its abundance and diversity, brown quartz has a wide variety of uses, including:
– Jewelry – Smoky quartz, tiger’s eye, and citrine are popular brown gemstones. Morion is used for mourning jewelry. Rutilated quartz is a unique jewelry stone.
– Carvings – Cairngorm has been carved into collectible figurines and ornaments for centuries. Other brown quartz like smoky and tiger’s eye are also used.
– Crystal Healing – In crystal healing, smoky quartz and citrine are claimed to have grounding, energizing, and detoxifying properties.
– Sculpture – The banded structure of tiger’s eye makes an attractive sculptural stone. It is often carved into eggs, spheres, and figurines.
– Cabochons – Morion and hawk’s eye are popular materials for cabochon gemstones with strong chatoyancy.
– Beads – Chips and beads of smoky quartz, tiger’s eye, and citrine are used in beadwork crafts.
– Industrial Uses – Ground brown quartz has uses as an abrasive, filter material, and specialty sand.
– Interior Design – Polished brown quartz slabs are used for countertops, walls, floor tiles, and backsplashes. Morion and smoky quartz make dramatic dark brown to black accents.
How Brown Quartz Is Graded
Gem quality specimens of brown quartz are graded according to the 4Cs:
– Color – More saturated and intense shades of brown are more valuable. Morion and cairngorm command higher prices than pale smoky quartz.
– Clarity – Transparent stones without inclusions receive higher grades. Opaque material is less valued.
– Cut – Smokey quartz, citrine, and tiger’s eye are often fashioned as faceted gems. Smooth, symmetrical faceting improves brilliance.
– Carat – Larger brown quartz stones are more rare and valuable than small ones. Gems over 5 carats are considered quite large.
For industrial purposes, brown quartz is graded based on physical properties important for the application, such as grain size, angularity, structural strength, and chemical purity.
How to Identify Brown Quartz
Here are some simple tests to identify various types of brown quartz:
– Hardness – Quartz has a hardness of 7 on the Mohs scale, able to scratch glass and most metals. This distinguishes it from softer brown minerals like calcite and amber.
– Luster – The vitreous luster of quartz appears glassy or pearly. Tiger’s eye has a silky luster due to asbestos fibers.
– Crystal form – Quartz often forms six-sided prisms. Smoky quartz and citrine may have terminated points.
– Cleavage – Quartz lacks cleavage planes due to its crystalline structure. Fractures show conchoidal patterns rather than flat planes.
– Acid test – Quartz is unaffected by acid. A drop of nitric acid will produce no reaction. In contrast, calcite will fizz vigorously.
– Density – Pure quartz has a density around 2.65 g/cm3. Brown varieties may have slightly lower densities due to substitutions in the crystal structure.
– Inclusions – Fibrous inclusions identify tiger’s eye. Rutile needles indicate rutilated quartz.
– Optics – Many brown quartz varieties exhibit chatoyancy or asterism effects due to fibrous structures.
Conclusion
Brown quartz encompasses a diverse range of varieties including smoky quartz, cairngorm, morion, citrine, tiger’s eye, hawk’s eye, brown amethyst, and rutilated quartz. The different brown colors arise from natural radiation exposure and the presence of impurities like iron, aluminum, and rutile needles. While found worldwide, certain locations are renowned for their brown quartz specimens. These attractive and abundant minerals have many uses from jewelry to industry. With proper identification tests, brown quartz can be reliably distinguished from look-alike minerals like calcite and zircon. The many shades and patterns make it a unique and fascinating gem material.
