Stone types and terms ( repost)

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*Stone types and terms*

 

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*Some basic ** information and list some common terms relating to

rocks, minerals and crystals .*

 

*Our main focus here is on the mystical spirits and healing energy

of crystals. A **little bit of the more mundane information **can

give us* *guidance . * *Rocks can be placed in three groups for

convenience :*

 

*Igneous rocks* :

 

*Include Granite, rhyolite, obsidian, and basalt among others.

**Igneous rocks** are formed by the solidification of molten magma

that emerges via volcanic activity and emerges or erupts through vents

or fissures in the Earth's Crust The nature and properties of these

crystals vary greatly depending in part on the conditions under which

the magma solidified . fast cooling creates rocks that tend not to have

crystals slower cooling can give similar kinds of atoms trapped in the

magma time to find each other and form crystals . There are thousands of

different kinds of igneous rocks.*

 

 

*Sedimentary Rocks*

*Rocks such as limestone , sandstone, shales, halites coals, and

gypsum are formed by the accumulation of " sediments " these are fine

rock particles or fragments, skeletons of microscopic organisms or

minerals leached from rocks that have accumulated from weathering.

These sediments have been redeposited under water and were later

compressed in layers over time and are classed as either evaporative

(often water soluble ) or organic sedimentary rocks.*

 

*Metamorphic rocks*

*Rocks such as marble, slate , schist, gneiss and quartzite are formed

by the alteration of igneous and sedimentary rocks through heat and/or

pressure. These physical and/or chemical changes to rocks maybe

exemplified by the formation of marble from thermal changes that have

occurred to limestone.*

 

*What is the difference between a rock and a mineral?*

*A mineral is defined as a substance that must have all four of these*

*characteristics: It must be found in nature. It must not be made of

anything that has ever been alive (organic). It has the same chemical

makeup wherever it is found and its atoms are arranged in regular

patterns and form crystals. It is solid.*

 

*Rocks are sometimes defined as an aggregate or combination of one or

more minerals and the definition is extended to cover clay ,loose sand

and certain limestones.*

 

*Crystal*

*a crystal is a uniform body with a geometric lattice. the varying

structures of the lattice are the causes of the varying physical

properties of the crystals and therefore also of the minerals and gems.*

*Piezoelectricity is that quality by which electricity and sometimes

light is produced by compression . Many cultures and spiritual

traditions have used crystals in ritual, often striking them to produce

flashes of visible light.*

*Pyroelectricity is that quality of an electrified state or polarity

which is produced by variation in temperature. Quartz has both

piezoelectric and pyroelectric properties which means that the

polarity of quartz crystal will change when subject to pressure or

heat as well as when held.*

 

*Crystal Terminology*

 

* Asterism*

*Shining lines that cross one another like rays from a star, caused by*

*light reflected by a series of microscopic canals.*

 

* Chatoyancy*

* Bands of light and dark that vary in width and hue as the stone is

turned in the light.*

 

* Cleavage*

* A mineral's tendency to split when force is applied, leaving a flat*

*surface. This happens when there are layers of weakness within the

crystal.*

 

* Crypto crystalline*

*Composed not of a single crystal crystal but of many extremely small*

*crystals, fused together.*

 

* Dichroism*

*The way different colors or shades can be seen according to the angle*

*at which you look at the crystal.*

 

* Double Refraction*

*Light is split into two rays, producing a double image.*

 

* Inclusion*

*Any embedded foreign body, such as rutile crystals in Quartz, or an ant

in Amber.*

 

* Labradorescence*

* The colorful play of refracted light reflected from cleavage planes.*

 

* Optical Lens*

* Refracted light is bent so as to enlarge, reduce, invert, or otherwise

distort an image.*

 

 

 

 

* Mohs Scale of Hardness*

 

*One way gemstones are classified is by hardness, both scratch hardness

and cutting resistance while the Mohs scale of hardness developed by

Frederich Mohs (1773-1839) is made somewhat obsolete by modern

technology an idea of the general hardness of a stone and whether it is

brittle helps you to protect your stones from damage and can help with

identification from softest to hardest the Mohs scale*. * The Mohs

Scale of Hardness has 10 classifications, 1 is the softest, and 10 is

the hardest. The only mineral that is an exception to this is mercury,

which is liquid. The diamond is the hardest, rated 10. Your fingernail

is a 2, a pocket knife is about a 5-6, and a piece of glass is a

6-7.Each classification will scratch the one preceding it. *

 

 

*1 Talc*

*2 Gypsum*

*3 Calcite*

*4 Fluorite*

*5 Apatite*

*6 Orthoclase*

*7 Quartz*

*8 Topaz*

*9 Corundum*

*10 Diamond*

 

*Some minerals have varying hardness according to the direction you may scratch

them in, but typically this is either hardly detectable or an exception to the

rule. The following is a partial listing of

stones and their hardness classification:

 

1. Talc, Graphite: Can be scratched with a fingernail and by any stone rated 2+

 

2. Gypsum, Bismuth, Lepidolite, Chlorite: Can be scratched with a fingernail and

any stone rated 3+

 

3. Calcite, Celestite, Barite: Can be scratched with a knife and any stone rated

4+

 

4. Fluorite, Malachite, Platinum: Can be scratched with a knife and any stone

rated 5+. Will scratch any stone rated 3-.

 

5 Apatite, Dioptase: Can be scratched with a knife and any stone rated 6+. Will

scratch any stone rated 4-

 

6. Feldspar, Pyrite, Amazonite, Hematite: Can be scratched with a knife and any

stone rated 7+. Will scratch any stone rated 5-.

 

7. Quartz, Tourmaline: Will scratch glass and any stone rated 6-. Can be

scratched by stones 8+.

 

8. Topaz, Spinel: Will scratch glass and any stone rated 7-. Can be scratched

by stones 9-10.

 

9. Corundum (ruby, sapphire): Will scratch glass and any stone rated 8-. Can be

scratched by diamond.

 

10.Diamond: Will scratch glass and all stones 1-9*

 

 

 

*( Some of this is adapted from " The Handy Science Answer Book " and

from* *package notes from several little rock collection kits and

" Gemstones of* *the World " by Walter Schumann)*

 

* Peggy Jentoft*

 

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