Things to work on

Crystalline Material

ordered atomic arrangements, some repeating others not

Polycrystalline Material:

composed of aggregates of randomly oriented crystals or fibers (can see individual crystals)

Crypto-crystalline/ Microcrystalline Materials

composed of aggregates on sub-microscopic minerals (can’t see individuals)

lustre

Brilliancy of stone by reflected light & determined by amount of incident light reflected from surface

Gemstone Origin

where it was formed w/ in the earth \n

Gemstone occurrence

where gems are found when its mined (not formed)

Gemstone locality

country or area where gem is found

Colored gem mining: \n

Placer, Eluvial & unconsolidated gravels

Diamond Mining:

Open pit kimberlite (low heat flow) or lamprolite (high heat flow) pipes & Placer deposits, river & beach gravels

Lapidary for cabochons polishing comp.

1. Cerium oxide
2. Aluminum oxide
3. Diamond grit
4. Carborundum
5. Rottenstone

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Jam-Peg Method

* wooden block w/ tapered holes @ differing heights & Fast & efficient

Mechanical

* Used for calibrated stones

**bruting (Shaping)**

* Girdle shaped by rubbing diamond against diamond (on lathe)

Crystal Growth:

* Crystallization from aqueous or molten solution

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Rapid cooling

* small crystals & /or microcrystalline masses

Properties that vary with direction

1. Hardness
2. Cleavage
3. Color
4. Optical properties

Axis of symmetry

rotation

Plane of symmetry

mirror images

Fibrous/ Columnar habit

Series of slender prisms

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Ex: Kyanite, Calcite

Prismatic

Main faces parallel to C-Axis

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Ex: Tourmaline, Quartz, zircon

Cruciform

Cross shaped b/c of twinning

Enantiomorphic

Mirror image habit & optical characteristic

- Right & left handed forms

Filiform Capillary

Hair like/ thread like

\- Fine formations

Foliated Micaceous

Layered structure that parts in thin sheets

Hemihedral

Only has 1⁄2 of full # of faces in symmetry

Hemimorphic

Different forms @ opposite ends of axis of symm. - (1 side different form than other)

Mamillary

Rounded intersecting contours

Pseudo- Hexagonal

Resumbles hexagonal due to cyclic twinning

Reticulation

Net like crystal growth

Sphenoid

Wedge Shaped

Scalenohedron

6-sided bipyramid w/ unequal sides

Isomorphic

identical external forms but differ chemically

Isomorphic Replacement

replacement of 1element in mineral by another (original structure maintained)

Polymorph

minerals differ in shape but have same internal composition

Pseudomorph

mineral has adopted external form other than its normal habit by copying shape of original crystals

Basel pinacoid

top & bottom pinacoid

3 origin of twinning

* Growth Twin
*  Transformation Twin
* Deformation Twin

Growth Twin

Accident growth where a new crystal is added to a existing crystal face \n

– Interpenetrant or contact

Transformation Twin

pre-existing crystal transforms due to change in heat & pressure

Deformation Twin

Atoms pushed out of place & make a symmetrical arrangement

Polysynthetic Twinning

* ̈  Type of multiple or repeated twin

lamellar

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*- Contact twin*

Carlsbad Twin

* Mirror plane, rotated around an axis

*- interpenetrant twin*

Manebach Law

* Mirror twin
* ̈  ONLY MONOCLINIC GEMS

*- contact twin*

Swallow Tail

* Mirror twin
* ̈  ONLY MONOCLINIC GEMS

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*- contact twin*

Japanese Law

* Due to accidents during growth (growth twin)
* Trigonal Crystal system!

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*- contact twin*

Dauphine Law

* Pseudo-hexagonal habit
* ̈  Right or left-handed
* ̈  Due to transformation

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*interpenetrant twin*

Brazil Law

* Twin axis rotation
* ̈  Pseudo-hexagonal habit

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*- interpenetrant twin*

Staurolite Law (cruciform twinning)

* Staurolite forms in orthorhombic system
* ̈  Cruciform habit

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*- interpenetrant twin*

Geniculate Twin

* Knee or elbow shape
* ̈  Mirror image

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*- contact twin*

Cyclical Tetragonal

* Not mirror image
* ̈  Tetragonal sections built up

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*contact twin*

**Flint Glass**:

* High lead content (increased dispersion & lower hardness)

**Crown Glass:**

* Soda lime composition

*Tektites*

natural glass - High silica content mixed w/ other elements

Moldavite

* made by heat from meteor impact – 75% silica

Basalt Glass

* Volcanic glass – 50% silica

Libyan Glass

*  Meteor glass – nearly pure silica

Detection of glass:

1. Strain patterns
2. Swirl lines
3. bubbles

Vulcanite

* Natural polymer
* imitate jet

Celluloid Plastic

*  wood or cotton chemically modified
* Imitates ivory or amber

Casein

* Milk protein mixed w/ formaldehyde
* Turquoise simulant, organic gems & mother of pearl

Bakelite

* Phenol formaldehyde resin
*  Imitates anything – easy to dye & texture

Polystyrene

* Plastic epoxy
* ̈  Imitates amber

what Ceramic imitation

Ex: turquoise, lapis & coral

“Synthetic” Lapis

* artificially produced ultramarine & hydrous zinc phosphates
* Opaque to transmitted light
* uniform color

“Synthetic” Coral

* crushed calciteno
* no wood structure
* uniform color

Green Chalcedony quartz imitating what

jade

yellow sapphire imitate what

yellow diamond

what is triplet loupe

* achromatic & aplanatic

microscope

stereo zoom bino microscope

4 natural inclusion

1. solid crystal
2. liquid
3. twinning
4. zoned growth

**Protogenetic inclusion formation**

* **pre-existing**) – present before host crystal formed

**Syngenetic inclusion formation**

* **(contemporary)** – inclusions formed @ same time as host crystal \n

**Epigenetic inclusion formation**

* **(post-contemporary)** – occurred after formation of host crystal

Paragenesis

order of crystallization of minerals

Corundum, Ruby and Sapphire inclusions

* Silk
* Healed fracture, Fingerprint
* Zircon Halos

Sunstone, Oligoclase, Feldspar inclusions

Goethite or hematite plates

Garnet, Almandine (Pyrope and Spessartine) inclusions

Rutile Needles

Grossular, Hessonite Garnet inclusions

Treacle effect

Quartz, Rock Crystal inclusions

* 2 Phase inclusions, gas and liquid


* Rutile inclusions, red or golden
* Actinolite inclusions, black

Spinel inclusions

Multitude of octahera

Topaz inclusions

* 2 and multiphase inclusions


* Incipient cleavage (rainbow boobs)

polariscope stones

* be able to transmit light)

polariscope interference fingures viewed where

Rainbow interference colors indicate stone is being viewed in direction of optic axis

Pleochroism

differential selective absorption - diff. colors indiff. directions

Dichroic stone

amyethst

Trichroic stone

Iolite

* nail head stone

cut too deep

* fish head

cut too shallow (cloudy like fish eye)

Refraction Index

ratio of angle between incident & refracted ray

Double Refraction:

optical doubling effect caused by splitting of light into 2

separate components by a DR materials

what is optically denser on refractometer

* prism acts as the optically denser material

stones on RI

polished transparent or opaque stones (must be polished!)

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& monochromatic light

chelsea filter light

Incandescent full spectrum

must be used

chelsea filter transmitted colors

* Chelsea filter transmits deep red & yellow green rays

*  “Basel” cleavage

* breaks off in ‘slices’ like bread

Parting

* “false cleavage
* directional weakness due to TWINNING, parallel to crystal faces

Toughness

Resistance to fracture or cleavage when pressure applied

Stability

Resistance to physical or chemical alteration due to light, heat or chemical attack

Durability

Resistance to physical or chemical forces hat destroy lustre or polish Resistance to daily wear

Opal triplets tops (3)

* quartz, plastic or glass