Calcite

Object/Artifact

-

Crater Rock Museum

Name/Title

Calcite

Entry/Object ID

78.63.223

Description

Chemical Composition: Carbonates Crystal System: Hexagonal System Description: Common Name: Calcite Chemistry: CaCO2 Group: Carbonates Location: Mexico Description: Calcite crystal mass on iron from Mexico. Iron base in black, ochre and red with white mineral, with a thick calcite and mineral layer in yellow, red and black with a top layer of well formed pale tan crystals of calcite. Physical Charateristics: :•Color is extremely variable but generally white or colorless or with light shades of yellow, orange, blue, pink, red, brown, green, black and gray. Occasionally iridescent. •Luster is vitreous to resinous to dull in massive forms. •Transparency: Crystals are transparent to translucent. •Crystal System is trigonal; bar 3 2/m •Crystal Habits are extremely variable with almost any trigonal form possible. Common among calcite crystals are the scalenohedron, rhombohedron, hexagonal prism, and pinacoid. Combinations of these and over three hundred other forms can make a multitude of crystal shapes, but always trigonal or pseudo-hexagonal. Twinning is often seen and results in crystals with blocky chevrons, right angled prisms, heart shapes or dipyramidal shapes. A notch in the middle of a doubly terminated scalenohedron is a sure sign of a twinned crystal. lamellar twinning also seen resulting in striated cleavage surfaces. Pseudomorphs after many minerals are known, but easily identified as calcite. Also massive, fibrous, concretionary, stalactitic, nodular, oolitic, stellate, dendritic, granular, layered, etc. etc. •Cleavage is perfect in three directions, forming rhombohedrons. •Fracture is conchoidal. •Hardness is 3 (only on the basal pinacoidal faces, calcite has a hardness of less than 2.5 and can be scratched by a fingernail). •Specific Gravity is approximately 2.7 (average) •Streak is white. •Other Characteristics: refractive indices of 1.49 and 1.66 causing a significant double refraction effect (when a clear crystal is placed on a single line, two lines can then be observed), effervesces easily with dilute acids and may be fluorescent, phosphorescent, thermoluminescence and triboluminescent. •Associated Minerals are numerous but include these classic associations: Fluorite, quartz, barite, sphalerite, galena, celestite, sulfur, gold, copper, emerald, apatite, biotite, zeolites, several metal sulfides, other carbonates and borates and many other minerals. •Notable Occurrences include Pugh Quarry, Ohio; Rosiclare, Illinois; Franklin, New Jersey; Elmwood, Tennessee; Brush Creek and other Missouri, Wisconsin, Kansas and Oklahoma localities, USA; Andreasburg, Harz Mountains and Saxony, Germany; Brazil; Guanajuato, Mexico; Cornwall, Durham and Lancashire, England; Bombay area of India; Eskifjord, Iceland; many African localities as well as others around the world with their own unique varieties. •Best Field Indicators are crystal habit, reaction to acid, abundance, hardness, double refraction and especially cleavage. Hardness: 7 Quartz Luster: Vitreous Rock Type: Sedimentary

Collection

Delmar Smith Mineral Collection

Acquisition

Accession

78.63

Source or Donor

Delmar Smith Crystal Collection

Acquisition Method

Donation

Dimensions

Width

3-3/4 in

Depth

4-3/4 in

Length

6 in

Location

Location

Display Case

FS-4

Room

Frieda Smith Hall

Building

Crater Rock Museum

Category

Exhibit

Moved By

Ian C.

Date

January 29, 2025

Notes

Major mineral groups installation

Location

Display Case

FS-5-A

Room

Frieda Smith Hall

Building

Crater Rock Museum

Date

January 3, 2024