Cochise College            Student Papers in Geology     
Geology Home Page                    physical geology  historical geology  planetary  gems

Roger Weller, geology instructor                                        

wellerr@cochise.edu
Quartz Family Gemstones-by Audrey LaClair
                                                
                                  Smoky Quartz

Smoky quartz is brown, black, or gray in color and is transparent.  It occurs most often in quartz veins where is has crystallized inside rock cavities called vugs.  It can occur as a secondary quartz crystal in cavities of vugs and cryptocrystalline quartz forming geodes. 

photo by R.Weller

The color of smoky quartz happens when rock crystal quartz are exposed to radiation.  This can occur from natural radiation or from radioactive rocks for an extended period of time.  Smoky quartz can be found in Brazil, the Himalayas, Switzerland, and Mexico  In the USA it is most often found in Colorado, but can also be found in Nevada, Arkansas, and California.

Smoky quartz has been used for ornamental and religious objects as well as gemstones.  Sometimes, the very dark brown color of the quartz is called morion.  Smoky quartz that is faceted has been called smoky topaz in the past.  But apparently, there is no such thing as smoky topaz.  In fact, it is illegal to refer quartz as a topaz. 

It is said that smoky quartz has kidney and pancreatic healing effects.  It is believed to have a relaxing effect, aides in mediation, and helps block negativity. 

photo by R.Weller

PHYSICAL PROPERTIES

·        Smoky Quartz chemical composition: SiO₂

·        Class: tectosilicate

·        Crystal system: Hexagonal-Rhombohedral; 32 (trigonal-trapezohedral)

·        Crystal habit: Macroscopic crystals commonly occur as horizontally striated hexagonal prisms terminated by a combination of positive and negative rhombohedrons forming six sided pyramids. Prism faces and/or rhombohedral terminations may be lacking, poorly developed or predominant resulting in diverse possible crystal habits. Trigonal tapezohedral faces can occur in the upper right or left of alternating prism faces identifying right or left handed crystals, respectively.

·        Twinning: Dauphine twin with c the twin axis, Brazil twin with {1120} the twin plane, Japanese twin is rare with {1122} the twin plane.

·        Specific gravity: 2.65

·        Index of refraction: 1.54-1.55

·        Birefringence: maximum of 0.009

·        Pleochroism: distinct

·        Hardness: 7

·        Color: brown to gray to black

·        Luster: vitreous

·        Transparency: transparent

·        Cleavage: none

·        Fracture: conchoidal

·        Streak: white

from http://www.mineralminers.com/html/smqminfo.htm
 

References:

http://www.bestcrystals.com/smoky.html
http://www.kamalkapoor.com/crystals/smoky_quartz.asp
http://www.mineralminers.com/html/smqminfo.htm
http://www.gemhut.com/smoky.htm