Fluorite/Calcite

Object/Artifact

-

Crater Rock Museum

Name/Title

Fluorite/Calcite

Entry/Object ID

78.63.284

Description

Chemical Composition: CaF2, Crystal System: Cubic or Isometric S Description: Common Name: Fluorite Group Name: Halides Chemistry: CaF2 Location: Illinois Description: Purple fluorite mass of rectangular crystals, with occasional white to off-white calcite crystals embedded on surface. PHYSICAL CHARACTERISTICS: Color is extremely variable and many times can be an intense purple, blue, green or yellow; also colorless, reddish orange, pink, white and brown. A single crystal can be multi-colored. Luster is vitreous. Transparency: Crystals are transparent to translucent. Crystal System: Isometric; 4/m bar 3 2/m Crystal Habits include the typical cube and to a lesser extent, the octahedron as well as combinations of these two and other rarer isometric habits. Always with equant crystals; less common are crusts and botryoidal forms. Twinning also produces penetration twins that look like two cubes grown together. Cleavage is perfect in 4 directions forming octahedrons. Fracture is irregular and brittle. Hardness is 4 Specific Gravity is 3.1+ (average) Streak is white. Other Characteristics: Often fluorescent blue or more rarely green, white, red or violet and may be thermoluminescent, phosphorescent and triboluminescent. Associated Minerals are many and include calcite, quartz, willemite, barite, witherite, apatite, chalcopyrite, galena, sphalerite, pyrite and other sulfides. . Best Field Indicators are crystal habit, color zoning, hardness (harder than calcite, but softer than quartz or apatite), fluorescence and especially the octahedral cleavage. Fracture: irregular Hardness: 4 Flourite Luster: Vitreous Occurrence: Fluorite may occur as a vein deposit, especially with metallic minerals, where it often forms a part of the gangue (the worthless "host-rock" in which valuable minerals occur) and may be associated with galena, sphalerite, barite, quartz, and calcite. It is a common mineral in deposits of hydrothermal origin and has been noted as a primary mineral in granites and other igneous rocks and as a common minor constituent of dolostone and limestone. Fluorite is a widely occurring mineral which is found in large deposits in many areas. Notable deposits occur in Germany, Austria, Switzerland, England, Norway, Mexico, and Ontario in Canada. Large deposits also occur in Kenya in the Kerio Valley area within the Great Rift Valley. In the United States, deposits are found in Missouri, Oklahoma, Illinois, Kentucky, Colorado, New Mexico, Arizona, Ohio, New Hampshire, New York, Alaska and Texas. Flourite has been the state mineral of Illinois since 1965. At that time, Illinois was the largest producer of fluorite in the United States; however, the last Illinois mine closed in 1995. The largest documented single crystal of fluorite was a cube 2.12 m in size and weighed ~16 tons Notable Occurrences include in addition to those mentioned above Cumberland, England; Spain; China; Brazil; Morocco; Bancroft, Ontario, Canada; Naica, Chihuahua, Mexico; Germany; Elmwood, Tennessee; Rosiclare, Illinois; Fort Wayne, Indiana; Pugh Quarry and Wood County, Ohio; Nancy Hanks Mine, Colorado and many other USA localities as well as many other localities from around the world Rock Type: Sedimentary Specific Gravity: 3.1 Streak: white Variety: The many colors of fluorite are truly wonderful. The rich purple color is by far fluorite's most famous and popular color. It easily competes with the beautiful purple of amethyst. Often specimens of fluorite and amethyst with similar shades of purple are used in mineral identification classes to illustrate the folly of using color as the sole means to identify minerals. The blue, green and yellow varieties of fluorite are also deeply colored, popular and attractive. The colorless variety is not as well received as the colored varieties, but their rarity still makes them sought after by collectors. A brown variety found in Ohio and elsewhere has a distinctive iridescence that improves an otherwise poor color for fluorite. The rarer colors of pink, reddish orange (rose) and even black are usually very attractive and in demand. Most specimens of fluorite have a single color, but a significant percentage of fluorites have multiple colors and the colors are arranged in bands or zones that correspond to the shapes of fluorite's crystals. In other words, the typical habit of fluorite is a cube and the color zones are often in cubic arrangement. The effect is similar to phantomed crystals that appear to have crystals within crystals that are of differing colors. A fluorite crystal could have a clear outer zone allowing a cube of purple fluorite to be seen inside. Sometimes the less common habits such as a colored octahedron are seen inside of a colorless cube. One crystal of fluorite could potentially have four or five different color zones or bands

Collection

Delmar Smith Mineral Collection

Acquisition

Accession

78.63

Source or Donor

Delmar Smith Crystal Collection

Acquisition Method

Donation

Dimensions

Width

2-3/16 in

Depth

2 in

Length

3-5/16 in

Dimension Notes

Dimension taken at widest points

Location

Location

Shelf

CS-F-1

Room

Curation Storage

Building

Crater Rock Museum

Category

Storage

Moved By

Curator

Date

February 21, 2024