The word 'crystal' is derived from the ancient Greek word κρύος (krýos) for 'frost', but comes from the ancient Greek κρύσταλλος (krýstallos) for 'clear ice', and later in Greece as 'rock crystal'. Composed of silica, the building block of Arkansas' rock crystals, it represents the most abundant crystal-forming mineral in our planet's continental crust. In its purest form as silicon dioxide (SiO2), quartz crystals epitomize rare and beautiful gem materials, and the gleaming crystaals from Arkansas are some of the most coveted on Earth. Its mineral form, quartz includes two distinct groups: cryptocrystalline and macrocrystalline. Cryptocrystalline or 'hidden crystals' are silicate rocks with nearly invisible crystal structures that include gem materials like jasper, agate, bloodstone, and carnelian. It is the macroscrystalline type however, that comprises those minerals with visible crystals that include citrine, amethyst, and rock quartz -- the prize of Arkansas's Ouachita Mountains.

The Ouachita Mountains extend from Central Arkansas into Eastern Oklahoma and represent one of the most important sources of quartz crystals on Earth producing large quantities of crystals for more than 200 years. Although spectacular quartz crystals have been found across the North America, Arkansas is the sole site where large-scale mining of quartz crystals operates. Most of these mines are located in Montgomery County, however increasingly mines are found in adjacent counties (i.e. Saline, Garland). Rivaled only by Brazil and Madagascar in the 19th Century, records indicate that mining has een active in the Ouachitas since the 1850s. The prominent gemologist for Tiffany & Company, George Frederick Kunz (1890) wrote that Arkansas' crystal mining generated more than $10,000 in 1898.

In Garland County, a rock crystal arrowhead was found at an archaeological site dating to 9000BC. Various artifacts have since been identified across Arkansas however, rock crystal mining has only been recorded in the region in the past two centuries. Commissioned by Thomas Jefferson to explore and chronicle the Washita River and hot springs in Arkansas, trip leaders William Dunbar and George Hunter made references to quartz crystals from the Little Missouri River Valley in what was then the Arkansas' Ouachita Mountains (c. 1804). In 1819, the explorer-geographer Henry Rowe Schoolcraft wrote,

“One of the most noted localities of this mineral west of the Mississippi River is the Hot Springs of Ouachita in Arkansaw Territory. At this place numerous pieces of quartz have been found, very pure and transparent, and beautifully crystallized" (1819).

Then in 1930, Ocus Stanley started modern quartz mining in the Mount Ida area in Montgomery County, with as many as 500 people employed there at the height of mining operations by 1980 -- considered the peak of quartz mining in Arkansas Nichols (1999).

The Ouachita Fold and Thrust Belt represents an important orogenic, or mountain building belt in North America, and the birthplace of Arkansas' rock crystals. This mountainous region extends 220 miles from Arkansas into eastern Oklahoma, and is underlain by an extensive anticline with its oldest beds of sandstone and shale found at its middle (Paradise 2012). The Ouachita Mountains are composed of highly deformed strata dating from 300 to 500 million years ago (Cambrian to Pennsylvanian). However, quartz crystal development is an epigenetic process occurring after the emplacement of the rock; Ouachita quartz growth occurred 240-280 million years ago (Engel 1951). It is through silica-rich hydrothermal vapor, liquids, and movement that the crystals grow over millions of years. Each crystal's growth begins at the simple molecular stageenlarging as more silica is added. When silica saturation temperatures, and pressures vary, atoms then combine in a variety of atomic arrangements and crystal shapes. As theories of quartz crystal development emerged in the 19th century, laboratory research confirmed its hydrothermal growth when in 1845, Karl von Schafhäutl recorded the first micro-crystalline quartz synthesis through a hydrothermal process using a Papin Vessel (pressure cooker). His process employed a silica-rich, high-pressure aqueous environment that was similar to the natural process found the Arkansas quartz crystal occurrence (Von Schafhäutl 1845). It was this pioneering investigation that confirmed early geologic theories of quartz crystal growth. Arkansas' quartz crystals are naturally found in pockets or vugs inside quartz-rich veins in weathered sandsto, stained by iron oxides that produce a characteristic brown color. In other quartz producing areas (i.e. Brazil these crystals may form in exceptionally large crystal pockets or pegmatites that take shape during the final phase of cooling magma. Pegmatites are rare in Arkansas, although sizeable crystals have been recorded since the early 1800s, some up to 300 pounds (Kunz 1892, Engel 1951). In smaller veins, the quartz develops into whitish seams, while larger veins enable the growth of larger relatively colorless and transparent crystals. Distinctive of Arkansas quartz crystals is the Dauphiné (doh-FEEN-eh) habit or surface form. Forming from the hexagonal crystal family, quartz crystals typically develop in six-sided prisms. The Dauphiné habit displays one or two enlarged rhombic faces of the prism terminal; it was named after Dauphiné, the Alpine region near Grenoble (Smith 1996) (Figure 3). Other quartz regions in the US (i.e. California, New York) rarely exhibit the Dauphiné as often as the Arkansas rock crystal. Kunz discussed widespread mining in Arkansas with crystal-lined cavities occasionally exceeding 30' by 6'.

"Wagonloads of these crystals were taken to Hot Springs and Little Rock by the farmers who do considerable blasting to secure them" (Kunz 1892: 110). He commented about the colorless nature and transparency of rock crystal in New York, Colorado, and Arkansas, however regarding the Ouachita quartz, he wrote that … 'Usually only half of the crystal is clear' (Kunz: 112, 1892). The most sought-after crystals are colorless and clear, although some may contain minor brownish limonite inclusions. Milky crystals are collected if the habit is clearly defined, and some may be artificially irradiated to produce a dark grey, smoky color. Surface characteristics can include parallel striations perpendicular to the crystal prism, while surface irregularities or habit structures, common in rock quartz from other regions (i.e. Tessin habit), are relatively absent in the Arkansas crystals (Smith 1996).

In mineralogy and gemology, quartz is relatively difficult to scratch, with a Mohs scale hardness of 7 (between apatite: 6 and topaz: 8) and the measure of brilliance -- its refractive index -- of 1.55 between feldspar (moonstone): 1.54 and beryl (aquamarine): 1.56. As a gemstone, quartz represents one of the most varied gems with macrocrystal varieties of citrine (orange), amethyst (purple), smoky (grey), and rose (pink) in addition to numerous microcrystal varieties including jasper (deep red), sard (brown), carnelian (orange), and aventurine (green). Nonetheless, through history it was rock crystal in its colorless, transparent form that has been so widely coveted, and few sites in North America regularly produce such brilliant specimens as the Arkansas crystals. . In 1967, the Arkansas  Legislature made the rock quartz crystal the official State Mineral (Paradise 2012).