Maryland State Gemstone
Patuxent River Stone
Patuxent River stone is a local variety of agate, found only in Maryland. Agate is a layered, multicolored variety of chalcedony. Chalcedony is a catchall term that includes quartz gemstones with microscopic crystal structure. Agate is composed of silicon and oxygen, with iron and aluminum oxides sometimes present.
Patuxent River stone may be a case of agate forming through fossilization of organic material, but this origin for the stone is disputed. Agate most commonly forms in rounded nodules or veins. Often, centuries of water have washed the outer surface away to reveal the pattern inside. When this is not the case, the crust must be cut open to view the stone’s inner beauty. Tiny quartz crystals called drusy often form inside the stone, especially in agates with hollow cavities. Since unpolished specimens of agate are dull, they are polished to bring out their full beauty.
Agate has hundreds of variety names, and new ones are introduced every year. Some of the more common varieties are fire, blue, blue lace, banded, carnelian, Lake Superior, thunder egg, and turritella agates. Patuxent River stone, or Patuxent River agate, is said to be composed of fragments of petrified bone that were filled in with silica and clay over 100 million years ago. Recently found specimens reportedly show a link to dinosaur bones.
Because Maryland is the only place Patuxent River stone occurs, it was chosen as the state gem. It also reflects two of the state colors, red and yellow. This designation did not come without controversy, however. Some geologists and other experts allege that the Patuxent River stone is not actually petrified dinosaur bone. This agate was designated the official gemstone of Maryland on October 1, 2004.
The name of this mineral comes from the site where it was originally reported, the Achates River, or Á÷Üôçò in Greek, which is now known as the Dirillo River in Sicily, Italy. The Greek naturalist and philosopher Theophrastus discovered agates sometime between the 4th and 3rd centuries BCE. Agates were widely used in the ancient world. Patuxent River agate was named for a tributary of the Chesapeake Bay.
FORMATION AND OCCURRENCE
Agates are normally associated with volcanic lava rocks but are also found in some metamorphic rocks. Silica-rich water percolates through the rock, escaping as gas and depositing traces of the silica in the rock’s crevices. Layers are formed and eventually the rounded nodules called agates result.
Patuxent River stone is found only in Maryland, in the narrow region between Washington, D.C., and Baltimore.
Because of its abundance, durability, and beauty, chalcedony was one of the earliest raw materials used by humans. The earliest recorded use was for projectile points, knives, tools, and containers such as cups and bowls. Early humans made weapons and tools from many varieties of chalcedony including agate, agatized coral, flint, jasper, and petrified wood. Agate, along with petrified wood, was then elevated from functional use as tools, vessels, and weapons to gem status, being used for decorative and religious purposes.
From antiquity through the Renaissance period, collecting bowls made of agate was a popular hobby. In fact, this hobby is what led to the growth of the gemstone industry in the Idar-Oberstein district of Germany, one of the world’s leading centers for gemstone cutting and trading.
Today, agate is chiefly made into stones and used for ornamental purposes, such as in brooches and pins, pendants and charms, beads, mosaics, and dream catchers. Agate is one of the most varied and most popular gemstones. Patuxent River stone is suitable for use as a gemstone, for carving, and as a geological specimen. Agates also have industrial and practical applications, such as letter openers, inkstands, mortars, and pestles.
Agate has been believed for centuries to protect the wearer or holder of the stone from a wide variety of dangers and to bring good fortune. Because it has been known and used by humans for millennia, the supposed benefits of agate are innumerable and cross into many cultures.
Agate is the mystical birthstone for September and the birthstone for the zodiac sign of Gemini. Agate is given for the 12th and 14th wedding anniversaries.
Chemical Formula: SiO2
Crystal Structure: Trigonal
Hardness (Mohs): 7; lower in impure varieties
Color: Clear (pure agate; Patuxent River Stone occurs in red to yellow)
Transparency: Transparent (pure agate; Patuxent River Stone can be opaque)
Birefringence: +0.009 (B-G interval)
Refractive Index: 1.544-1.553 - Dr +0.009 (B-G interval)
Density: 2.65 (pure agate)
Some data courtesy of the Mineralogical Society of America
Author: World Trade Press