Rutilated Quartz (or Tourmalinated Quartz if inclusions are Tourmaline)

Hardness: 7 on Mohs scale (for quartz); Color: colorless, white, smoky, or yellowish quartz with black, golden, red, or green needle-like inclusions; Luster: Vitreous; Crystal Structure: Hexagonal (for quartz); Cleavage: None; Specific Gravity: 2.65 for quartz (may vary slightly with inclusions)

Rutilated Quartz forms when rutile (titanium dioxide) needles grow within quartz crystals. This typically occurs in hydrothermal veins and pegmatites. The growth of the rutile needles can happen during the primary growth of the quartz or through later metamorphism. The geological age varies depending on the specific deposit, but it is found in formations billions of years old to much younger ones.

Predominantly used in jewelry, especially as beads, cabochons, and faceted stones. Valued for its unique visual appeal created by the needle-like inclusions. It is also collected by mineral enthusiasts.

The inclusions can be extremely fine and dense, giving the quartz a metallic shimmer, or they can be thicker, distinct needles. The most prized Rutilated Quartz often features golden, reddish-brown, or black rutile needles. 'Star' rutile patterns can sometimes be observed. If the inclusions are black and thicker, they might also be tourmaline (often called Tourmalinated Quartz), which has a similar appearance but different chemical composition.

In the field, it is identified by the characteristic needle-like, hair-like, or fibrous inclusions within a typically clear to smoky quartz host. The color and pattern of these inclusions are key. It is commonly found in Brazil (Minas Gerais), Australia, Russia, Norway, Switzerland, Pakistan, and the United States (especially Arkansas). For collectors, identifying the type and quality of the inclusions is crucial; well-defined, aesthetically pleasing inclusions are most desirable. A scratch test against a known mineral of Mohs hardness 7 (like another quartz piece) can help confirm the quartz host.