Difference between revisions of "Synthetic cubic zirconia"
(added refractometer) |
(Added "ly" to wide) |
||
(14 intermediate revisions by 2 users not shown) | |||
Line 1: | Line 1: | ||
{{synthetic cubic zirconia}} | {{synthetic cubic zirconia}} | ||
− | Synthetic cubic zirconia entered the market as a gemstone around 1976 and is till present the most | + | Synthetic cubic zirconia (CZ) entered the market as a gemstone around 1976 and is till present the most widely used diamond simulant. Although cubic zirconia is found in nature (as minute crystals inside [[zircon]]), the more stable variant of zirconia crystallizes in the monoclinic system (baddeleyite).<br /> |
− | The main means of syntheses is through the "[[skull crucible]]" | + | The main means of syntheses is through the "[[skull crucible]]" aka "skull melting" method. |
==Chemical composition== | ==Chemical composition== | ||
Line 10: | Line 10: | ||
==Diagnostics== | ==Diagnostics== | ||
− | As synthetic cubic zirconia (CZ) is mainly used to imitate diamond one can expect the main separation techniques to concentrate on distinguishing between the two. | + | As synthetic cubic zirconia (CZ) is mainly used to imitate [[diamond]] one can expect the main separation techniques to concentrate on distinguishing between the two. |
+ | |||
+ | ===Color=== | ||
+ | |||
+ | Synthetic cubic zirconia is produced in a large array of colors, from colorless to black. Many coloring agents, including rare earth elements, are added to the source powder. | ||
+ | * Cesium: yellow, orange, red | ||
+ | * Copper, iron, nickel, praseodymium, titanium: yellow, amber, brown | ||
+ | * Erbium, europium, holmium: pink | ||
+ | * Chromium, thulium, vanadium: green | ||
+ | * Cobalt, manganese, neodymium: lilac, violet, purple, blue | ||
+ | |||
+ | ===Diaphaneity=== | ||
+ | |||
+ | Transparent to opaque. | ||
===Refractometer=== | ===Refractometer=== | ||
− | The optical properties of CZ vary slightly depending on which stabilizer is used (yttria or calcium oxide). | + | Cubic zirconia has an RI that can not be measured with a standard gemological refractometer. There are however other tools available, as the Hanneman-Hodgkinson refractometer or the Brewster angle meter, to determine the RI of CZ. |
+ | |||
+ | The optical properties of CZ vary slightly depending on which, and how much, stabilizer is used (yttria or calcium oxide). | ||
* Yttria stabilized cubic zirconia: RI = 2.171, dispersion = 0.059 | * Yttria stabilized cubic zirconia: RI = 2.171, dispersion = 0.059 | ||
* Calcium oxide stabilized cubic zirconia: RI = 2.177, dispersion = 0.065. | * Calcium oxide stabilized cubic zirconia: RI = 2.177, dispersion = 0.065. | ||
Line 21: | Line 36: | ||
* The "dot test" will show a ring around the culet if the stone is cut to diamond brilliant proportions. | * The "dot test" will show a ring around the culet if the stone is cut to diamond brilliant proportions. | ||
* The "tilt test" will show leakage. | * The "tilt test" will show leakage. | ||
+ | |||
+ | ===Polariscope=== | ||
+ | |||
+ | CZ may show anomalous extinction. | ||
+ | |||
+ | ===Specific gravity=== | ||
+ | |||
+ | The SG of CZ is about twice that of diamond (3.52) and loose stones will have a higher "heft".<br /> | ||
+ | As with the refraction indices, the SG of CZ varies between stabilizers used. | ||
+ | * Yttria stabilized cubic zirconia: SG = 5.95 | ||
+ | * Calcium oxide stabilized cubic zirconia: SG = 5.65 | ||
+ | |||
+ | ===Hardness=== | ||
+ | |||
+ | * Yttria stabilized cubic zirconia: hardness = 8.25 (Mohs' scale) | ||
+ | * Calcium oxide stabilized cubic zirconia: hardness = 8.5 (Mohs' scale) | ||
+ | |||
+ | ===Luminescence=== | ||
+ | |||
+ | Colorless CZ stabilized by calcium oxide will show a yellow fluorescence. | ||
+ | |||
+ | ==Phenomena== | ||
+ | |||
+ | Color change synthetic cubic zirconia is not uncommon and may show dramatic changes in natural/incandescent lightning.<br /> | ||
+ | Opalline (milky) CZ's are also produced. These are mainly opaque. | ||
+ | |||
+ | ==References== | ||
+ | |||
+ | * [http://www.google.com/patents?id=9MoEAAAAEBAJ&printsec=abstract&zoom=4&dq=fianit The 1972 patent to create "Fianit" (synth. cubic zirconia) from Lebedev] | ||
+ | * [http://www.amazon.com/gp/product/0750658568?ie=UTF8&tag=gemsandwhywelove&link_code=as3&camp=211189&creative=373489&creativeASIN=0750658568 Gems Their Sources, Descriptions and Identification'' 4th Edition (1990) - Robert Webster (6th ed.)] | ||
+ | <br /> | ||
+ | <br /> | ||
+ | '''[[Visual_Optics&action=edit| Visual Optics: Needs Content!]]'''<br /> | ||
+ | '''Next: [[Video_presentations| Video Presentations]]''' | ||
+ | <br /><br /> | ||
+ | '''[[Table_Of_Contents| Return to the Table of Contents]]''' |
Latest revision as of 16:35, 13 January 2010
Synthetic cubic zirconia | |
---|---|
Chemical composition | Zirconium dioxide - ZrO2 |
Crystal system | Cubic |
Habit | Columnar |
Cleavage | |
Fracture | |
Hardness | 8.25 - 8.5 |
Optic nature | Isotropic |
Refractive index | 2.171 - 2.177 |
Birefringence | None |
Dispersion | High, 0.059 - 0.065 |
Specific gravity | 5.65 - 5.95 |
Lustre | |
Pleochroism | None |
Synthetic cubic zirconia (CZ) entered the market as a gemstone around 1976 and is till present the most widely used diamond simulant. Although cubic zirconia is found in nature (as minute crystals inside zircon), the more stable variant of zirconia crystallizes in the monoclinic system (baddeleyite).
The main means of syntheses is through the "skull crucible" aka "skull melting" method.
Contents
Chemical composition
Zirconia has the chemical formula ZrO2, this material however will not crystallize in the cubic system through syntheses. A stabilizer of yttria or calcium oxide needs to be added to the source powder in order to let it crystallize as isotropic crystals.
Diagnostics
As synthetic cubic zirconia (CZ) is mainly used to imitate diamond one can expect the main separation techniques to concentrate on distinguishing between the two.
Color
Synthetic cubic zirconia is produced in a large array of colors, from colorless to black. Many coloring agents, including rare earth elements, are added to the source powder.
- Cesium: yellow, orange, red
- Copper, iron, nickel, praseodymium, titanium: yellow, amber, brown
- Erbium, europium, holmium: pink
- Chromium, thulium, vanadium: green
- Cobalt, manganese, neodymium: lilac, violet, purple, blue
Diaphaneity
Transparent to opaque.
Refractometer
Cubic zirconia has an RI that can not be measured with a standard gemological refractometer. There are however other tools available, as the Hanneman-Hodgkinson refractometer or the Brewster angle meter, to determine the RI of CZ.
The optical properties of CZ vary slightly depending on which, and how much, stabilizer is used (yttria or calcium oxide).
- Yttria stabilized cubic zirconia: RI = 2.171, dispersion = 0.059
- Calcium oxide stabilized cubic zirconia: RI = 2.177, dispersion = 0.065.
The values of CZ are above the limits of the standard gemological refractometer. There are however a few other tests one can perform.
- The "dot test" will show a ring around the culet if the stone is cut to diamond brilliant proportions.
- The "tilt test" will show leakage.
Polariscope
CZ may show anomalous extinction.
Specific gravity
The SG of CZ is about twice that of diamond (3.52) and loose stones will have a higher "heft".
As with the refraction indices, the SG of CZ varies between stabilizers used.
- Yttria stabilized cubic zirconia: SG = 5.95
- Calcium oxide stabilized cubic zirconia: SG = 5.65
Hardness
- Yttria stabilized cubic zirconia: hardness = 8.25 (Mohs' scale)
- Calcium oxide stabilized cubic zirconia: hardness = 8.5 (Mohs' scale)
Luminescence
Colorless CZ stabilized by calcium oxide will show a yellow fluorescence.
Phenomena
Color change synthetic cubic zirconia is not uncommon and may show dramatic changes in natural/incandescent lightning.
Opalline (milky) CZ's are also produced. These are mainly opaque.
References
- The 1972 patent to create "Fianit" (synth. cubic zirconia) from Lebedev
- Gems Their Sources, Descriptions and Identification 4th Edition (1990) - Robert Webster (6th ed.)
Visual Optics: Needs Content!
Next: Video Presentations
Return to the Table of Contents