Ruby is a red variety of the mineral corundum, chemically composed of aluminum oxide (Al2O3). Its signature crimson color is created by trace amounts of chromium that substitute for aluminum within the crystal lattice structure. This substitution is responsible for the stone’s characteristic red hue, which can range from pinkish-red to a deep, vivid blood-red. The mineral possesses exceptional durability, ranking 9 on the Mohs scale of mineral hardness, second only to diamond.
Primary Global Ruby Deposits
The world’s most commercially significant ruby sources are defined by their unique geological environments, which yield distinct stone qualities. For centuries, Myanmar, formerly Burma, was the dominant source, particularly the Mogok Stone Tract, known for producing the highly prized “pigeon’s blood” rubies. These stones often form in marble, a metamorphic rock, and are characterized by an intense red color that appears to glow due to strong fluorescence caused by low iron content.
A more recent but equally important source is Mozambique, whose Montepuez deposit has become a leading global supplier in the 21st century. These rubies, also typically found in metamorphic formations, often exhibit high clarity and a vibrant color, though they may require heat treatment to enhance their appearance. Southeast Asia remains a consistent source, with deposits in Thailand and Cambodia yielding rubies formed in basaltic rock. The presence of iron in these basalt-hosted rubies often results in a darker, brownish-red color and less natural fluorescence compared to their marble-hosted counterparts.
Accessible Locations for Amateur Prospecting
While the major global deposits are reserved for commercial mining, several accessible locations allow the public to experience the thrill of finding a ruby. The Cowee Valley in Macon County, North Carolina, is the most famous location in the United States, offering numerous “fee-to-dig” mines. At places like the Cherokee Ruby & Sapphire Mine, visitors can sift through buckets of screened gravel taken directly from gem-rich alluvial deposits.
These commercial operations provide the necessary equipment and processed material for easy searching by amateur rockhounds and tourists. Beyond North Carolina, rubies and their close relatives, sapphires, are also found in alluvial deposits in states like Montana and Alabama. Prospecting in riverbeds, or secondary deposits, is possible because the hard corundum crystals resist weathering and concentrate in gravel bars where water currents slow down. The rubies found in these public access areas may not be the large, transparent, gem-quality stones of commercial fame, but they provide beautiful specimens for collectors.
Recognizing Raw Ruby in the Field
Identifying a raw ruby crystal requires attention to its specific physical properties, which distinguish it from other red minerals like garnet or spinel. In its natural form, corundum often exhibits a hexagonal crystal habit, appearing as terminated tabular prisms or barrel-shaped crystals. A raw ruby can be distinguished by its exceptionally high density, with a specific gravity ranging from 3.97 to 4.05 grams per cubic centimeter, making it feel notably heavier than most similar-sized stream gravel.
The stone’s luster ranges from vitreous to subadamantine, giving it a glassy or slightly brilliant appearance in natural light. A simple hardness test can confirm the mineral’s identity, as only diamond is capable of scratching ruby. Furthermore, the presence of chromium causes many rubies to fluoresce a bright, intense red when exposed to long-wave ultraviolet light. This characteristic glow can make them stand out even in a pile of mixed stones. In the field, rubies are often found alongside associated minerals like mica, feldspar, and zoisite, indicating the metamorphic or igneous host rock from which they originated.
Legal and Ethical Considerations for Collecting
Before embarking on any gem collecting trip, it is necessary to determine the legal status of the land. Collecting on private property requires explicit, written permission from the landowner to avoid charges of trespass or theft. Federal lands, such as those managed by the Bureau of Land Management (BLM), generally permit non-commercial collection of reasonable amounts of mineral specimens using hand tools.
However, areas administered by the National Park Service strictly prohibit the removal of any rocks or minerals without a highly specific scientific permit. Prospectors should always check with the local administrative office, as regulations vary by state and agency. Fines can be substantial for unauthorized collection. Responsible collecting also means minimizing environmental impact by backfilling any holes and avoiding disturbance of sensitive ecological or archaeological sites.