Hornblende

Object/Artifact

-

Crater Rock Museum

Name/Title

Hornblende

Entry/Object ID

78.62.216

Description

Chemical Composition: Ca2(Mg, Fe, Al)5 (Al, Si) Crystal System: Monoclinic System Description: Common Name: Hornblende Chemistry: Ca2(Mg, Fe, Al)5 (Al, Si)8O22(OH)2 Class: Silicates Location: Location Unknown Description: Delmar describes this specimen as a crystal hornblende(amphbole), surrounded by mica (hydrous silicate). A large green and black crystal to the side (hornblende), is surrouned on most sides by brown and tan sheet mica, showing perfect clearage. PHYSICAL CHARACTERISTICS: Color is almost always black to dark green. •Luster is vitreous to dull. •Transparency: Crystals are generally opaque but thin crystals or exceptional specimens can be translucent. •Crystal System is Monoclinic; 2/m •Crystal Habits include short stocky prismatic crystals as well as long thin crystal forms. Crystals can have a hexagonal cross-section although rarely symmetrical. The typical termination, if seen, appears as the two faces of a dome but is actually two of the four faces of a prism. Also found granular, massive and occassionally acicular aggregates. •Cleavage is imperfect in two directions at 56 and 124 degrees. •Fracture is uneven. •Hardness is 5 - 6. •Specific Gravity is approximately 2.9 - 3.4 (somewhat above average for translucent minerals) •Streak is brown to gray. •Other Characteristics: pleochroic in translucent speciments. Large crystals have an almost striated or grainy appearance. •Associated Minerals are quartz, feldspars, augite, magnetite, micas and many medium grade metamorphic minerals. •Notable Occurrences are numerous and include Bancroft, Ontario; Norway; Bohemia; Mt. Vesuvius, Italy and New York, USA. •Best Field Indicators are crystal habit (especially cross-section), color and cleavage. Fracture: uneven Grain Size: Medium Hardness: 5 Apatite Luster: Vitreous Pressure: Moderate Rock Color: Dark Rock Origin: Post-depositional Rock Type: Sedimentary Specific Gravity: 2.9-3.4 Streak: Brown to Gray Temperature: Moderate to high

Collection

Delmar Mineral Collection

Acquisition

Accession

78.62.212

Dimensions

Height

5 in

Length

4-1/8 in

Dimension Notes

Dimension taken at widest points

Location

Location

Cabinet

H-2 front

Wall

North

Building

Storage (old gift shop upstairs)

Category

Permanent