Physical Properties & Specific Gravity - Science test 2

Conversion of Carats to Grams

1 Carat = 0.20 of a gram
5 Carats = 1 gram

1/2 carat = points?

1/2 carat = 0.50 carat = 50 Points

1/4 carat = points?

1/4 carat = 0.25 carats = 25 points

Heft

how heavy/ dense the material feels in hand

- stone of the same carat can be different sizes due to their density - due to atoms in 1 material more closely packed than in another

Density

ratio between volume & weight (how heavy the atoms are)

- how tightly packed the atoms are vs the weight

heavier density = atoms?

Heavier density = more tightly arranged atoms

Specific gravity

density of a substance relative to the density of WATER

Specific gravity formula

SG = Weight of substance (cts)
-------------------------------------------
Weight of a equal volume of water

what does 1 CC (cubic cm) of water = to gram

1cc of water = 1 gram

i.e gram x 5 = carats (1 gram=5 carats)

archimedes' principle

the apparent loss in weight of a material immersed in a fluid = equal to the weight of the displaced fluid

i.e: object in water displaces the same amount of water as weight of object

Hydrostatic Method

Weight of material in air compared with its weight in water

- only used for stones above 1 ct

Process of hydrostatic method

(6 steps)

1. weigh gemstone in air (A)
2. fill beaker 2/3 with DISTILLED WATER
3. place on bridge & insert cage/ wire
4. reset scale to 0
5. hang & immerse stone
6. weigh stone in water (B)

Formula for finding specific gravity with hydrostatic method

SG = A - weight in air
------
A - B - weight in water (B)

What to watch out for when doing hydrostatic method
(3)

1. stone is clean & free of grease
2. stone free of air bubbles
3. stone is 1 ct or more

High density Liquids

(2 used)

Di-idomethane & 1-Bromonaphthalene (bro-mo-nap-pha-lane)

Stone hovers 1/2 way in high density solution

SG same as solution (approx. 3.05)

Stone sinks in high density solution

SG greater than 2.65

Stone floats on top of high density solution

SG less than approx. 3.33

Stone substitution formula

used when want to change a gemstone & need to calculate weight of gemstone

weight of current stone X SG of desired stone ———————————————————————————————————
SG of current stone

Hardness

Hardness of minerals measured on Mohs scale, resistance to abrasion

- relative scale - not equally spaced

Hardness scale from 1 to 10

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

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Directional Hardness

some stones harder in 1 direction than in another

- differential hardness in different directions - like wood grain

example of directional hardness

- diamonds can be cleaved in directions parallel to octahedral crystal faces

- Kyanite hardness of 5 in basel plane & hardness of 7 in prismatic direction

Hardness Testing

DESTRUCTIVE TEST

- testing needles of various hardness used to compare what needles scratch a unknown material