There are a few different types of crystals that can display a reddish brown color. Some of the most common reddish brown crystals include agate, jasper, sunstone, carnelian, and sard. The specific mineral composition, trace elements, and structural properties of each crystal can impact the exact shade and intensity of the red-brown hue.
Agate
Agate is a popular semi-precious silica mineral that is part of the quartz family. It is characterized by its unique banded patterns and various colors. Red and brown agates are very common. The red-brown color in agate is caused by trace amounts of iron oxide. The bands, stripes, or spots of reddish brown color can range from pale pinkish orange to deep burgundy red-brown. Botswana agate and Laguna agate are two well-known varieties that exhibit rich red-brown banding.
| Agate Property | Details |
|---|---|
| Chemical composition | Silicon dioxide (SiO2) |
| Color cause | Iron oxide impurities |
| Mohs hardness | 6.5 – 7 |
| Crystal system | Trigonal |
The unique color banding of agate is due to trace mineral impurities that are arranged in layers when the agate forms inside gas vesicles of volcanic rock. So agate’s alternating color patterns result from changing trace mineral contents during the crystal growing process.
Jasper
Jasper is another microcrystalline quartz mineral that is heavily included with various impurities which give it distinct coloring. There are many named jasper varieties based on color and patterning such as bloodstone, poppy jasper, and brecciated jasper. Red jasper specifically exhibits rich red, orange, and brown colors due to inclusions of iron oxide. Picture jasper displays stunning reddish-brown patterns that resemble desert landscapes. Red jasper is found in many locations worldwide including the western United States, India, and Egypt.
| Jasper Property | Details |
|---|---|
| Chemical composition | Silicon dioxide (SiO2) |
| Color cause | Iron oxide inclusions |
| Mohs hardness | 6.5 – 7 |
| Crystal system | Trigonal |
The rich reddish brown hues of jasper are created as it crystallizes in cavities of volcanic rock where iron, hematite, and other minerals become trapped within the structure. The patterns and colors of jasper are unique based on these inclusion compositions which vary for each geological formation.
Sunstone
Sunstone is a plagioclase feldspar mineral that exhibits a bright reddish-orange shine due to inclusions of hematite or copper. Occasionally sunstone forms in larger transparent crystals, but more often it occurs in granular aggregates with a reddish-brown color. Notable sunstone deposits have been found in Oregon, Canada, Norway, and Russia. The reflective inclusions of hematite platelets cause a schiller effect as sunstone is moved in the light.
| Sunstone Property | Details |
|---|---|
| Chemical composition | Calcium aluminum silicate (SiO4) |
| Color cause | Hematite and copper inclusions |
| Mohs hardness | 6 – 6.5 |
| Crystal system | Triclinic |
The glittery inclusions within sunstone create a feldspar matrix that refracts and scatters light into bright flashes of orange and red-brown. Oregon sunstone in particular exhibits a rich reddish brown body color. The schiller effect from embedded hematite or copper platelets is a distinctive feature of high quality gemstone-grade sunstone.
Carnelian
Carnelian is a translucent orange to brownish-red variety of chalcedony quartz. Good quality carnelian has a rich reddish-brown color, like that of cornelian cherry wood. The color results from trace iron oxide impurities. Significant carnelian deposits have been found in India, Brazil, Uruguay, Germany and in the United States. Carnelian has been used since antiquity for carvings, beads, inlays and ornamental objects. It is also set into jewelry pieces.
| Carnelian Property | Details |
|---|---|
| Chemical composition | Silicon dioxide (SiO2) |
| Color cause | Iron oxide impurities |
| Mohs hardness | 6.5 – 7 |
| Crystal system | Trigonal |
The color saturation of carnelian varies based on the concentration of iron oxide and the way it is distributed within the microcrystalline quartz structure. Quality carnelian has an even distribution of iron impurities to create a uniform red-brown coloring without light or dark spots.
Sard
Sard is a deep orange-brown colored chalcedony quartz, named after the ancient Sardis region where it was first found. It is essentially carnelian with a darker more opaque brownish-red coloration. The color results from iron oxide impurities that form larger crystal clusters compared to the finer iron dispersal in carnelian. Significant sard deposits have been found in India, Czech Republic, Slovakia, Brazil, and United States. Sard has been used for intaglio engravings, signet rings, beads, and other ornamental objects since ancient times.
| Sard Property | Details |
|---|---|
| Chemical composition | Silicon dioxide (SiO2) |
| Color cause | Iron oxide impurities |
| Mohs hardness | 6.5 – 7 |
| Crystal system | Trigonal |
The difference between sard and carnelian is subtle – sard has a darker, richer red-brown color that is opaque due to larger iron oxide crystal clusters within the microcrystalline quartz. Carnelian exhibits a lighter orangey-brown hue with more translucency from the finer dispersion of iron impurities.
Conclusion
In summary, some of the most common reddish brown crystals include varieties of microcrystalline quartz such as agate, jasper, carnelian, and sard. Their iron oxide impurities result in shades of red-brown coloration. Sunstone is a plagioclase feldspar that also exhibits a distinctive reddish-brown hue due to hematite and copper inclusions. The specific mineral structure and arrangement of trace element impurities determine the intensity and patterning of the red-brown colors in these crystals.
When searching for quality red-brown crystals, look for those with rich uniform color saturation without unsightly light or dark spots. Stones with interesting multi-colored banding or landscape patterns are especially prized. Reddish brown crystals can make beautiful additions to rock collections, jewelry pieces, and other ornamental objects.
