Home
Categories
Send a question
Activities
Resources
Virtual Field Trip
Glossary
Geology of Communities
Dynamic Earth
Hot Spots
Geology in the Classroom
GeoToolbox
Especially For Teachers
Hall of Fame
Geological Milestones
 
 
spacer

Rocks and Minerals

How are quartz crystals formed in igneous rocks?




Quartz crystals are formed in igneous rocks in basically two different ways, either directly from the magma, or hydrothermally after the main rock has solidified. When the crystals form directly from the magma, what you see would be an almost-interlocking mosaic of the shapeless quartz grains with the other minerals that solidify from the magma - the micas (biotite and muscovite), the feldspars.

When the quartz forms as a result of hydrothermal processes, what you will commonly see is a quartz vein through the rock, with well-formed quartz crystals occurring in the middle of the vein. These quartz crystals would have the shape of a six-sided prism with a six-sided point on one end (could have both ends pointed in rare crystals). These quartz veins and crystals form as a later process after the main igneous rock has crystallized. The cooled body of rock would have openings in it, probably caused by cooling, jointing, or fracturing, and these openings are filled with a silica (quartz) rich fluid that passes through the openings and then solidifies. The amount of time for crystallization and the size of the opening will determine whether the quartz vein will develop the well-formed crystals.

Linda Ham, Nova Scotia Dept. of Natural Resources

Return to questions
   

    Last Modified: 2004-12-10