Mica Schist

Object/Artifact

-

Crater Rock Museum

Mica shist

Mica shist

Name/Title

Mica Schist

Entry/Object ID

2014.1.149

Description

Assemblage Zone: pegmatite dikes Chemical Composition: Fe3O4 Crystal System: Monoclinic System Description: Common Name:Mica Schist Group Name: Sheet silicate (phyllosilicate) Chemistry: Fe3O4 Location: Upland, CA Description: A small slab of Mica schist, biege in color. Crystals are layered and perfectly alligned. There is a silvery sheen on the flat surfaces. PHYSICAL CHARACTERISTICS: The mica group of sheet silicate (phyllosilicate) minerals includes several closely related materials having close to perfect basal cleavage. All are monoclinic, with a tendency towards pseudohexagonal crystals, and are similar in chemical composition. The highly perfect cleavage, which is the most prominent characteristic of mica, is explained by the hexagonal sheet-like arrangement of its atoms. The word "mica" is derived from the Latin word mica, meaning "a crumb", and probably influenced by micare, "to glitter". Crystal habit: platy, micaceous, also compact massive. Foliated sheets can be (rarely) aggregated into globular or botryoidal form, also cryptocrystalline. Distinct crystals are uncommon and are typically tabular with a book-like form with basal planes, showing a hexagonal or diamond-shaped outline. Prism faces are striated horizontally and frequently taper. Twinning: occaisional twinning on {110}, a twin axis in the {001} composition plane forms the complex mica twin. Specific gravity: 2.2 - 3.3 (Biotite 2.7-3.3, lepidolite 2.2-3.3, muscovite 2.77-2.88, zinnwaldite 3.0) Index of refraction: 1.53-1.70 (Biotite 1.56-1.70, lepidolite 1.52-1.59, muscovite 1.55-1.62, zinnwaldite 1.53-1.59) Birefringence: .018-.070 (Biotite .04-.07, Lepidolite .018-.038, muscovite .036-.049, zinnwaldite .035) Pleochroism: Biotite is strongly pleochroic in shades of brown or green, fuchsite in shades of green, lepidolite pale violet or green, muscoviteis colorless, zinnwaldite in pale yellow and brown to reddish-brown Hardness: 2.0 -4.0, hardness is greater perpendicular to the cleavage (Biotite 2..5-3.0, Lepidolite 2.5-4.0, muscovite 2.0-2.5, zinnwaldite 3.0) Color: Biotite is dark green, brown, or black (sometimes yellow), fuchsite is an emerald green, Lepidolite is pink to lilac to light gray, muscovite is colorless to light shades of yellow, brown, red or green, zinnwaldite is yellow, brown or gray. Luster: vitreous, pearly, metallic Transparency: translucent, transparent in thin sheets Cleavage: perfect basal cleavage Streak: white Fracture: perfect basal cleava Hardness: 3 Calcite Luster: Vitreous Occurrence: Mica is widely distributed and occurs in igneous, metamorphic and sedimentary regimes. Large crystals of mica used for various applications are typically mined from granitic pegmatites. Until the 19th century, large crystals of mica were quite rare and expensive as a result of the limited supply in Europe. However, their price dramatically dropped when large reserves were found and mined in Africa and South America during the early 19th century. The largest documented single crystal of mica (phlogopite) was found in Lacey mine, Ontario, Canada; it measured 10×4.3×4.3 m and weighed about 330 tonnes. Similar-sized crystals were also found in Karelia, Russia. The British Geological Survey reported that as of 2005, Kodarma district in Jharkhand state in India had the largest deposits of mica in the world. China was the top producer of mica with almost a third of the global share, closely followed by the US, South Korea and Canada. Large deposits of sheet mica were mined in New England from the 19th century to the 1960s. Large mines existed in Connecticut, New Hampshire, and Maine. Scrap and flake mica is produced all over the world. In 2010, the major producers were Russia (100,000 tonnes), Finland (68,000 t), United States (53,000 t), South Korea (50,000 t), France (20,000 t) and Canada (15,000 t). The total production was 350,000 t, although no reliable data were available for China. Most sheet mica was produced in India (3,500 t) and Russia (1,500 t). Flake mica comes from several sources: the metamorphic rock called schist as a byproduct of processing feldspar and kaolin resources, from placer deposits, and from pegmatites. Sheet mica is considerably less abundant than flake and scrap mica, and is occasionally recovered from mining scrap and flake mica. The most important sources of sheet mica are pegmatite deposits. Sheet mica prices vary with grade and can range from less than $1 per kilogram for low-quality mica to more than $2,000 per kilogram for the highest quality. Rock Type: Metamorphic Specific Gravity: 2.2 - 3.3 Streak: white Variety: The mica group represents 37 phyllosilicate minerals that have a layered or platy texture. The commercially important micas are muscovite and phlogopite, which are used in a variety of applications.

Collection

Delmar Smith Mineral Collection

Acquisition

Accession

2014.1

Source or Donor

Crater Rock Museum (unknown donors)

Acquisition Method

Gift

Dimensions

Width

1-3/4 in

Depth

11/16 in

Length

2-1/4 in

Dimension Notes

Dimension taken at widest points

Location

Location

Shelf

CS-E-1

Room

Curation Storage

Building

Crater Rock Museum

Category

Storage

Moved By

Curator

Date

February 23, 2024