A. Processes that create gemstones still going on in the Earth.

1. Earth is dynamic with a constantly changing "solid earth."

2. New gems created at different levels in the Earth.

a. Upper mantle is source of diamond, corundum (sapphire, ruby), peridot.

1) To form these minerals requires very high temperature and pressure only found in magma of upper mantle.

2) Molten magma finds weaknesses (fractures) in the crust and works its way to the surface.

3) Gemstones found at or near the surface are exposed through crustal movement and erosion.

b. Within crust, all gem-forming environments'related to magma and volcanic activity.~

1) Gems are found in previously molten magma.

2) Metamorphic deposits where temperature and pressure changes of pre-existing rocks caused by contact with magma chambers creates gems (contact metamorphism).

3) Pegmatites--one of richest sources of gem minerals.

a) Volcanism causes hot, watery, mineral-rich solutions.

i. Geysers, hot springs

ii. Pegmatites where hot solutions are trapped in crustal fractures.

· Hot solutions contain dissolved exotic elements needed to create gemstones

· Open fractures and mobile fluids allow optimum crystal growth (2- to 3-foot long crystals common, up to 12 feet)

· Examples: opal, turquoise (near copper deposits), beryl

1. Weathering very important in freeing crystals from rock matrix of the original deposit (primary deposit).

2. Secondary deposits: alluvial and placer deposits.

a. Gem crystals more resistant to weathering than rock matrix.

1) Gemstone characteristics of hardness and durability allow them to survive weathering and be concentrated in gravels.

2) Alluvial and placer deposits.

a) Formed by rivers, floods, or running water.

b) Most important source of gems.

II. John White, curator of minerals at Smithsonian Institute, defines minerals and gemstones as the same thing, with gemstones being the better quality specimens.

III. John Sinkankas relates the thrill of finding gemstones and being the first human to see a gemstone created 1000's to millions of years ago.

A. Overview: Sapphire--Montana

Tourmaline--California, Maine

Beryl--Utah

Turquoise--Arizona

Peridot--Arizona

Sunstone- -Oregon

B. Ponderosa Mine, Oregon- -Sunstone

1. Occurs in knots of labradorite feldspar in an oxidized (weathered) basalt flow.

2. Also found in Finland, Norway, India, and basalt flows in Hawaii.

3. All surface mining with bulldozers and then examined on tables with screens.

C. Harris Mine, Central Utah--Red Beryl

1. Red beryl is a variety of beryl

a. Also called red emerald (misnomer)

b. Aquamarine

c. Emerald

d. Golden or heliodor

e. Morganite (pink)

2. Utah only location in world for red beryl.

3. Found in rhyolite lava flows.

D. Murfreesboro, Arkansas

1. Only operating diamond mine in U.S.

2. Fee digging open to public.

E. Tourmaline

1. Mt. Mica Mine, Maine

a. Tourmaline in pegmatites

b. Green, cranberry tourmalines

2. San Diego, California

a. Tourmalines in pegmatites

b. Himalaya Mine produces rubellite (red tourmaline) and bi colored tourmaline.

1) Crystal development of bi-colored tourmaline.

a) First schorl (black, iron-rich tourmaline) deposited.

b) Iron is used up (none available) and other elements replace iron in the growing crystal.

i. Causes the crystal to clarify.

ii. Color gets redder and redder in transition zone.

iii. Blue cap on red tourmaline.

2) Blue cap on red tourmaline unique to Himalayan Mine (only location in world).

F. El Dorado Bar Mine, Montana--Sapphires

1. Sapphires found in placer deposits.

a. River gravels (gravel bars) deposited by ancient Missouri River.

b. Gravel bars found 200 feet above present river.

c. Weathered from basalts (primary deposits) and accumulated over a long period of time in placers (river sand and gravels).

2. Mined by bulldozers and then examined in tables with screens.

H. San Carlos Apache Tribe Mine, Arizona--Peridot

1. Peridot crystals found as knots (nodules) in basalt flows.

2. Also found In basalt flows in Hawaii.

1. Found in vein deposits that formed in fractures associated with copper deposits.

2. Hand-mined with picks and shovels.

3. Turquoise

a. Name from mining in Persia (Iran) and marketed in Turkey.

b. Gem lore--bring's luck and money.

1. Cutting faces on stones to emphasize light reflection and color.

2. Best for transparent stones to emphasize refractive qualities.

a. Light from above is bent upon entering the stone, reflects inside the stone, and leaves through the top facet (table).

b. Stones generally harder and more brittle.

B. Cabochons--Dome Top

1. Used with softer, more opaque material.

2. Best used to emphasize color.

C. Example: Sunstone from Ponderosa Mine is faceted, cabochoned, or beaded.

D. Evaluation and Cutting Process

1. Evaluate for use as:

a. mineral specimen

b. cabochon

c. faceting

2. Factors

a. Crystal size

1) length

2) diameter

b. Color

c. Surrounding material

1) free-floating crystal

2) crystal imbedded jn rock matrix

d. Clarity

1) inclusions

2) surface blemishes

3. Process

a. Cut rough crystal

b. Grind facets or cabochon

c. Finish polishing

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