Hexagonal Hexagonal CRYSTALSCRYSTALS

Audrey FreyChris Vu

Ivy NguyenYifan Zhang

Period 2

What is a crystal?What is a crystal?• Most solids made of crystals• In a crystal, a group of atoms is arranged in a specific geometric pattern, called

a unit cell. This pattern is repeated throughout the solid• Overall shape of crystal depends on the arrangement of the atoms. (“What is a

crystal?”)• In hexagonal crystal unit cell, 12 atoms are involved. • Unit cells have eight faces; six atoms form a regular hexagon base on one end

and six other atoms form another hexagon base on the other end. Bases line up so edges are parallel and form rectangular faces when connected.

• Horizontal base edges are equal to each other and not equal to the vertical edges, which can be shorter or longer than the base edges.

• Angles between base edges are 120°; angles between base edge and vertical edge 90°

• Unlike other crystal systems, hexagonal crystals have eight faces • Hexagonal crystals have a six-fold axis of rotation ("Crystalline Structures | Crystal

Lattice Structures." )

Different Views of Hexagonal Crystal Structures

("Crystalline Structures | Crystal Lattice Structures." )

SOME EXAMPLES OF HEXAGONAL CRYSTAL STRUCTURES INCLUDE...

Beryl Beryl BeBe33AlAl22(SiO(SiO33))66• Highly prized and relatively rare• All types are used as gemstones, also sources of beryllium• Some beryl gemstones include Emerald, Aquamarine, Heliodor or Golden Beryl,

Morganite, Goshenite (“Beryl”)• Name derived from Greek “berylloss”, which encompasses any green gemstone.• Used to ward off demons and evil spirits, cure eye injuries, treat heart and spine

disorders, protect travelers, promote cheerfulness and marital love, retard laziness, maintain youthfulness, and increase sincerity. ("Beryl Facts, Information and Description." )

• Found in Brazil, Pakistan, Russia, Madagascar, Nigeria, Colombia, Nevada, and California

• Can be found attached to the walls of cavities in topaz-rock, which consists of finely granular quartz and small topaz crystals. Beryl can also be found in layers of loose material of topaz-rock just beneath the soil.

• Beryl priced per carat according to clarity, color, and size. Exceptional stones of five carats or more have sold for as much as $25,000 per carat.

• Synthetic emerald can be produced in labs, and costs much less than natural emerald. ("Beryl Facts, Information and Description." )

TYPES OF BERYL("Gems and Minerals Photograph Gallery." )

RED BERYL HELIODOR

EMERALD

HELIODOR

AQUAMARINE

Quartz SiO2• Very common• Once used primarily for decorative purposes. The Egyptians used it as a

turquoise replacement. Native Americans and Ming dynasty artists used it for jewelry. (“History of Quartz”)

• Now used for electronics, grinding stones, and a component of glass.• Quartz crystals vibrate or tick exactly 60-seconds per minute electricity is

applied, so they are used to keep time in watches and computers (“Quartz crystal”)

• Mined in Arkansas, Brazil, Mexico• Quartz is especially common within granites, and can also be observed in

metamorphic rocks. • Quartz veins often form where fluid passes through rock fractures.• Quartz makes up 12% of the Earth’s crust by volume. ("THE MINERAL Quartz." )• Because there is such a wide variety of quartz, there is no set price that

quartz sells for.• Quartz is used widely in the construction industry as gravel, at low cost.• For quartz jewelry points on the other hand, prices range from $30 to

$300 a pound. (“Quartz Crystals: Putting a value on quartz crystals." )

•

TYPES OF Quartz(”The Mineral Quartz" )

Rock Crystal

Smoky Quartz

Citrine

Rose Quartz

Graphite CGraphite C• Relatively common• Used primarily as a lubricant and as pencil lead • Also used for batteries, friction materials, and brushes in electrical motors• Mined in New York, Texas, Mexico, and Greenland. Synthetic graphite is

made from coke and pitch. • Graphite is found in mesomorphic rocks such as coal, slate or shale

deposits. It is also found in underground veins believed to have previously been crude oil that was compressed over time.

• Graphite is very cheap due to its abundance.• The substance is a good lubricant because it is so slippery. This

slipperiness is caused by its variation on the hexagonal crystal structure. Instead of having strong bonds connect all the atoms, only the bases in the crystal are strongly connected and make layers of carbon. Weak Van der Waals forces hold the layers together, but allow them to slide over each other (see following slide for an illustration)

("Graphite (C) – Classifications, Properties and Applications of Graphite." )

Above: A piece of graphite("Graphite (C) – Classifications, Properties and Applications of Graphite." )Right: Carbon atoms in graphite are strongly attracted to each other within a layer, but are weakly attracted between layers, allowing layers to slide over each other. (“Graphite (C) – Classifications, Properties and Applications of Graphite.“)

WORKS CITEDWORKS CITED"Beryl." Chard. 05 Feb 2007. Chard 24 Carat. 11 Feb 2007 <http://www.24carat.co.uk/berylframe.html>.

"Beryl." University of Texis at Austin. 03 Dec 2003. University of Texas at Austin. 11 Feb 2007 <http://www.geo.utexas.edu/courses/347k/redesign/gem_notes/Beryl/beryl_main.htm>.

"Beryl Facts, Information and Description." Beryl: Key facts. Jan 2006. Bernardine Fine Art Jewelry. 11 Feb 2007 <http://www.bernardine.com/gemstones/beryl.htm>.

"Crystalline Structures | Crystal Lattice Structures." Khulsey. 05 Feb 2007. KEVIN HULSEY ILLUSTRATION, INC. 11 Feb 2007 <http://www.khulsey.com/jewelry/crystalline_structures.html>.

Erickson, Jon. An introduction to fossils and minerals : seeking clues to the earth's past. New York: Facts on File, 2001.

"Gems and Minerals Photograph Gallery." Photograph Gallery. Jan 2007. Department of Earth & Planetary Science UC Berkeley. 11 Feb 2007 <http://ist-socrates.berkeley.edu/~eps2/wisc/jpeg/l9s16.jpeg>.

"Graphite (C) – Classifications, Properties and Applications of Graphite." Azom. May 3005. UKAS Accreditated Lab. 11 Feb 2007 <http://www.azom.com/details.asp?ArticleID=1630>.

"

Harrison, Karl. "Beryl." Mineral of the Month: March. Mar 1997. 3D Chem. 11 Feb 2007<http://www.3dchem.com/molecules.asp?ID=74>.

"History of Quartz." Jewelry Supplier. Jan 2006. Albuquerque 505 Wholesale Jewelry. 11 Feb 2007 <http://www.jewelrysupplier.com/2_quartz/quartz_history.htm>.

Marsh, Barry. "Graphite." School of Ocean & Earth Science. 2006. SOES. 11 Feb 2007<http://www.soes.soton.ac.uk/resources/collection/minerals/minerals/images/M01-Graphite.jpg>

"Quartz crystal." Computer Hope. July 2006. Computer Hope. 11 Feb 2007<http://www.computerhope.com/jargon/q/quartz.htm>.

“Quartz Crystals: Putting a value on quartz crystals." Rockhounding Arkansas. Jul 1998. Rockhounding Arkansas. 11 Feb 2007 <http://rockhoundingar.com/quartz/worth.html>.

"THE MINERAL Quartz." Galleries.com. 2006. Galleries.com. 11 Feb 2007<http://www.galleries.com/minerals/silicate/quartz/quartz.htm>.

"What is a Crystal?." Kiwi Web: Chemistry & New Zealand. 2007. Kiwiweb. 11 Feb 2007<http://www.chemistry.co.nz/crystals_defined.htm>.