Andradite var. demantoid

Object/Artifact

-

Crater Rock Museum

Name/Title

Andradite var. demantoid

Entry/Object ID

2004.1.40

Description

Assemblage Zone: pegmatite dikes Chemical Composition: Ca3Fe2(SiO4)3, Calcium ir Crystal System: Cubic or Isometric S Description: Common Name: Andradite var. demantoid Group Name: Garnets Chemistry: Ca3Fe2(SiO4)3, Calcium iron silicate Location: Ural Montains, Russia Description: Dark brownish black squared crystals. PHYSICAL CHARACTERISTICS: Color is typically greenish gray to green but also black, yellow and rarely colorless. Luster is vitreous. Transparency crystals are transparent to translucent. Crystal System is isometric; 4/m bar 3 2/m Crystal Habits include the typical rhombic dodecahedron. also seen is the 24 sided trapezohedron. Combinations of these forms are common and sometimes the rare faces of the hexoctahedron, a 48 sided crystal habit that rarely is seen by itself, can also combine with these other forms making very attractive, complex and multifaceted crystals. Massive occurrences are also common. Commonly forms crust that shows many rhombic faces Cleavage is absent. Fracture is conchoidal. Hardness is 6.5 - 7.5 Specific Gravity is approximately 3.8+ (above average for translucent minerals). Streak is white. Associated Minerals are micas, chlorite, diopside and serpentine. Other Characteristics: index of refraction is 1.89 (highest of the garnets).. Best Field Indicators are crystal habit, color, index of refraction and hardness Fracture: conchoidal Hardness: 7 Quartz Luster: Vitreous Occurrence: Notable Occurrences include Arizona; ural mountains in Russia; Italy and California Specific Gravity: 3.8 Streak: white Variety: Andradite, like other garnets, forms rounded crystals with 12 rhombic or 24 trapezoidal faces or combinations of these and some other forms. This crystal habit is classic for the garnet minerals. Andradite is the calcium iron garnet and forms in contact or regional metamorphic environments as does grossular, the calcium aluminum garnet. It is believed that these garnets form from the metamorphism of impure siliceous limestones. Andradite has many varieties based on color. Melanite is the black variety. Demantoid is the bright green variety and is sometimes cut as a gem. Topazolite is the yellow variety and is also occassionally cut as a gem.

Collection

Suomynona Mineral Collection

Acquisition

Accession

2004.1

Source or Donor

Suomynona Mineral Collection

Acquisition Method

Donation

Dimensions

Width

3-1/2 in

Depth

3 in

Length

4-1/2 in

Weight

2.66 oz

Dimension Notes

Dimension taken at widest points

Location

Location

* Untyped Location

RD-4

Category

Permanent

Moved By

Scott Longan

Date

August 25, 2009

Location

Container

middle

Drawer

bottom tier

Shelf

east side

Cabinet

case #58

Wall

south of center

Room

Delmar Smith Hall

Building

Crater Rock Museum

Category

Permanent