Identification of Rough Crystals

1-   Two Thing Are IMPORTANT For The Identification Of Crystals.

• Shape & Symmetry.
• Surface Features.

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2- Fold Symmetry   DIAMOND RHOBUS

3- Fold Symmetry  TRIANGLE

4- Fold Symmetry  SQUARE

5- Fold Symmetry  RECTANGLE

Internal Observation With Loupe

 Solid :

• Crystal
• Neddles
• Fiber

Liquid:

• Fingerprints.
• Undefined Shape can also be .
• if there is water , the surface will shine .

Gass:

• Bubbles , black rim around the bubble      <---- (glass)
• Donut Bubble

Note: If It Is Natural ,it can also be round   ....Naturally , there will be TadPad shape bubbles....

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What is External Observation in Gemology?

 External   Observation

  Rough:-

1. Horizontal  Striations 
2. Vertical  Striations
3. Trigons  Striations
4. Etch Pits 
5. Pits
6. Terrace Like Mark
7. Cavity
8. Material Emeded in cavity
9. Facture

Cut & Polish

1. Scratch
2. Polishig Lines
3. Abraded facet Edges
4. Chipping
5. Cleavage
6. Facture

What Is Dichcroscope?

 

The dichroscope is an important pocket instrument used in the field of geology, and can be used to test transparent gemstones (crystals). Experienced geologists using pleochroism can successfully detect gemstones from other artificial stones using this instrument.

Calcite dichroscope

There are two types of dichroscopes available: calcite and polarizing. Of the two, calcite gives better results and is widely used by experienced gemologists. With the polarizing type, only one pleochroic color can be seen at a time. This makes the process time-consuming and difficult, though it is the most economical way to get results.

The dichroscope has been used since at least the start of the nineteenth century

what is Polariscope ?

WHAT IS POLARISCOPE ?

Polariscope is an instrument used in gemmology which helps to find if the gemstone is single refractive or double refractive and also allows determining the various crystal axis of the stone. ... A polariscope is made of two Polaroid plates that rotate, a power switch, a stone holder and a bottom light source.

1-
    DR is  Anisotropic = double refraction means (DR)
    SR is  Isotropic = single refractive =single colour mean (SR)
2-
   7 out of 6 CRYSTALLINE is  DR
    CRYSTALLINE Cubic System are SR

   Pollycrystalline Or Microcrystalline Gemstones  do  not blink and stay light during 360 degree

3-

 POLLYCRYSTALLINE GEMS  Stone stays  Light  through 360 rotaion in all orientaions.

Advantages

To Gemology
  GEMOLOGIST can Identify cleavage in rough and even cut stone hence in helps in the identification of the stone

To Lapidary

CLEAVAGE is Quicker than sawing  hardness direction can be find in DIAMOND
due to cleavage
   CONCHOIDAL FRACTURE
Citrin Quartz

How Can A tell Cleavage from A Freacture

Cleavage and fracture. When crystals break, they can either split leaving a clean, flat face called a cleavage plane, or fracture leaving a more rough, uneven surface. We can find out more about a crystal by looking at the way it breaks. Cleavageplanes form along the weakest area of mineral's structure

Can a mineral have a cleavage and fracture?

Cleavage and fracture differ in that cleavage is the break of a crystal face where a new face (resulting in a smooth plane) is formed, whereas fracture is the "chipping" shape of a mineral. All minerals exhibit a fracture, even those that exhibitcleavage

Cleavage & Fracture

CLEAVAGE & FRACTURE

Cleavage is the tendency of a mineral to break along smooth planes parallel to zones of weak bonding.

 Fracture is the tendency of a mineral to break along curved surfaces without a definite shape. These minerals do not have planes of weakness and break irregularly.

Hardness Pencils

• Hardness Test Should Be Started From The Least hard Pencil.
• Start From Smaller Number Softer To Harder Pencil TO Leave Only ONE Scratch.

Moh's Hardness Scale

                                                 Moh's Hardness Scale 

1. Talc 
2. Gypsum
3. Calcite
4. Flourite
5. Apatite
6. Feldspare
7. Quartz
8. Topaz
9. Corundum
10. Diamond