Mariposite is a distinctive green mineral. It is a type of chromian mica, which means its characteristic green hue comes from the presence of chromium in its chemical structure. This mineral often appears as veins or disseminated flakes within its host rock.
Mariposite’s Namesake Location
Mariposite is named after Mariposa County, California, its primary discovery location. Discovered in 1868, its presence during the California Gold Rush often indicated nearby gold deposits, guiding prospectors.
In Mariposa County, Mariposite is typically found within specific rock formations, particularly altered ultramafic rocks like serpentinite. Hot, mineral-laden fluids, often around 650°F, interacted with these serpentine bedrock formations, leading to the development of mariposite. This metamorphic rock is commonly observed as green and white material containing varying amounts of quartz, ankerite, and dolomite.
Global Occurrences and Geological Context
Beyond its namesake in California, Mariposite has been identified in various other locations worldwide. It can be found in other parts of the Sierra Nevada mountains in California, as well as in Marblemount, Washington. Globally, occurrences have been reported in Canada, where it is sometimes referred to as “virginite,” and across Europe. Further discoveries extend its known distribution to countries such as China, France, Ireland, Spain, Sweden, Japan, and Austria.
The presence of Mariposite in these diverse geographical areas points to a common geological context: it is typically associated with specific types of metamorphic rocks. It is often found in quartz-rich metamorphic rocks, including phyllites, schists, and gneisses. Furthermore, Mariposite is frequently linked to areas containing chromite deposits or altered ultramafic rocks, such as serpentinite, which provide the necessary chromium for its distinctive green color.
Formation and Characteristics
Mariposite’s formation is primarily a result of hydrothermal alteration and metamorphism. This process involves hot, aqueous fluids interacting with pre-existing rocks, chemically replacing original minerals with new ones. The presence of chromium is essential to Mariposite’s development, as it is a chromium-rich variety of mica. These fluids, often derived from metamorphic origins, introduce chromium into the rock, leading to the distinctive green coloration.
The mineral displays several identifiable physical characteristics. It has a vibrant green color, ranging from light to dark, often appearing as streaks or disseminated flakes within a white or gray host rock, commonly dolomitic marble or quartz. Mariposite exhibits perfect micaceous cleavage, meaning it can be split into thin, flexible sheets. Its hardness is relatively low, typically around 2.5 on the Mohs scale, making it a soft mineral. It often has a pearly, vitreous, or silky luster.