Is glass classified as a crystal?

Glass is not a type of crystal. Although crystal and glass may look similar in appearance, they have distinct differences in composition, physical properties, and manufacturing processes.

 

Composition:

• Crystal (Crystal):
  • Main Component: The main component of crystal is silicon dioxide (SiO2), which is a pure quartz crystal.
  • Additives: To increase the refractive index and luster of crystal, a certain proportion of lead (PbO) is usually added, and this type of crystal is called lead crystal. The lead content in lead crystal is usually above 24%, which makes the crystal have a higher refractive index and dispersion, thus showing a dazzling brilliance under light.

    

• Glass (Glass):
  • Main Component: The main component of glass is also silicon dioxide (SiO2), but in addition to this, it also contains other compounds, such as:
    • Sodium silicate (Na2SiO3): Provides chemical stability and workability to the glass.
    • Calcium silicate (CaSiO3): Increases the chemical stability and mechanical strength of the glass.
  • Additives: Glass may also contain other additives, such as:
    • Coloring agents: Used to change the color of the glass.
    • Clarifying agents: Such as sodium sulfate (Na2SO4), used to remove bubbles from the glass, making the glass more transparent.
    • Fluxes: Such as borax (Na2B4O7), used to lower the melting point of the glass, facilitating processing.

              

 

In summary, the main difference between crystal and glass is that crystal is a pure silicon dioxide crystal, while glass is a non-crystalline substance containing a variety of compounds. The lead added to crystal can improve its optical properties, while the additives in glass are used to improve its processability and appearance.

      Structure:

• Crystal (Crystal):
  • Crystal Structure: Crystal has a regular crystal structure, and its atoms are arranged in a specific geometric pattern. This orderly arrangement makes the crystal anisotropic, meaning that the physical properties (such as electrical conductivity, thermal conductivity, optical properties, etc.) may differ in different crystal directions.
  • Atomic Arrangement: In crystal, the atoms of silicon dioxide are arranged in a regular lattice, and this lattice structure gives the crystal a specific geometric shape and symmetry.
  • Long-range Order: The atomic arrangement inside the crystal is consistent on a macroscopic scale, and this long-range order is a characteristic of the crystal structure.

          

 

• Glass (Glass):
  • Amorphous Structure: Glass is an amorphous solid, and its atomic arrangement lacks long-range order. The atomic arrangement in glass is random and has no fixed crystal structure.
  • Short-range Order: Although glass lacks long-range order, the atomic arrangement may show a certain regularity in the local (short-range) area, and this local order is called short-range order.
  • Isotropy: Since the atomic arrangement in glass is random, its physical properties are basically the same in all directions, showing isotropy.

 

 

   How to tell if a chandelier is crystal or glass?

• Observe Bubbles: Glass may form bubbles inside during the manufacturing process because air is not expelled, while natural crystal often contains gas-liquid inclusions, not bubbles. Therefore, observing whether there are bubbles can be a basis for determining whether it is crystal.

 

• Luster and Refractive Index: The luster of crystal and glass is different. Glass contains PbO (lead oxide) to increase the refractive index, making glass products whiter and brighter, looking prettier than crystal. Crystal is anisotropic and shows four bright and four dark changes when rotated 360 degrees under a polarizing microscope, while glass is isotropic and turns completely dark when rotated 360 degrees under a polarizing microscope.

 

• Refractive Index: The refractive index of natural crystal is 1.544-1.553, and the birefringence is 0.009; glass has only one refractive index and no birefringence.

 

• Ultraviolet Fluorescence Reaction: Natural crystal has no fluorescence under long and short waves of ultraviolet light, while glass shows strong fluorescence.

 

• Touch Temperature: Natural crystal feels cool to the touch, while glass feels relatively warm to the hand.

 

• Sound: Tapping the surface of crystal and glass with a finger, the sound of crystal is crisp with a metallic sound, while ordinary glass has a dull sound.

 

• Hardness: The hardness of crystal is 7, while the hardness of glass is between 5-6. Scratching glass with crystal leaves a scratch that cannot be wiped off, and the crystal is not damaged; scratching crystal with glass leaves a slight scratch that can be wiped off, and the glass is damaged.

 

• Birefringence: Crystal has birefringence, while glass does not. Observing under a polarimeter, crystal shows changes of four bright and four dark, while glass does not show such changes.

 

     

 

• Luster and Color: Comparing under sunlight, high-quality crystal refracts bright colorful light, and the transition of light is very natural and rich. Glass refraction is incomplete and more dim. Comparing transparency under natural light, high-quality crystal has high transparency, showing a crystal-clear white, while ordinary glass or impure crystal may be yellowish or mixed with cyan.

Through the above methods, crystal and glass can be accurately distinguished.

Reference

1.  Stephen Lower. "Chem1 online textbook—States of matter". Retrieved 2016-09-19.

2. ^ Ashcroft and Mermin (1976). Solid State Physics.

3. ^ κρύσταλλος, Henry George Liddell, Robert Scott, A Greek-English Lexicon, on Perseus Digital Library

4. ^ κρύος, Henry George Liddell, Robert Scott, A Greek-English Lexicon, on Perseus Digital Library

5. ^ "crys·tal". The American Heritage Dictionary of the English Language. Retrieved 2023-06-17.