Glass
What is Glass?
Glass is made by quickly cooling molten material such as silica sand to prevent visible crystals from forming. It can be man-made or natural. It has widespread practical and technological use in creating windows, mirrors, lighting, drinking glasses, eyeglasses, fiber optics, and artistic creations such as stained glass. Glass making dates back to the earliest civilizations.
Uses & Applications
Glass can be natural or artificial in origin, though most that is sold today is artificially created. It is used for more than mirrors and windowpanes. Artisans create stunning works of art with the material. It can also be found in jewelry, often infused with dyes. Dishes and cookware are also made from glass. It is also used for packaging everything from food to perfumes and cosmetics.
Optical Properties
- Refractive Index
- 1.48-1.70
- Optical Character
- Isotropic
Discover Values
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The Meaning
Glass has been regarded as a magical stone for ages and it was commonly associated with the Divine. In Mesopotamia, where the history of glass starts, this material was worshiped as the embodiment of God. The material was so prized, that glassmaking in Mesopotamia was turned into an important ritual.
Key Characteristics
Formation of Glass
Glass can form naturally from volcanic magma. Obsidian is a common volcanic glass with high silica (SiO2) content formed when felsic lava extruded from a volcano cools rapidly. Impactite is a form of glass formed by the impact of a meteorite, where Moldavite (found in central and eastern Europe), and Libyan desert glass (found in areas in the eastern Sahara, the deserts of eastern Libya and western Egypt) are notable examples. Vitrification of quartz can also occur when lightning strikes sand, forming hollow, branching rootlike structures called fulgurites. Trinitite is a glassy residue formed from the desert floor sand at the Trinity nuclear bomb test site. Edeowie glass, found in South Australia, is proposed to originate from Pleistocene grassland fires, lightning strikes, or hypervelocity impact by one or several asteroids or comets.
Composition of Glass
The standard definition of a glass (or vitreous solid) is a solid formed by rapid melt quenching. However, the term "glass" is often defined in a broader sense, to describe any non-crystalline (amorphous) solid that exhibits a glass transition when heated towards the liquid state. Glass is an amorphous solid. Although the atomic-scale structure of glass shares characteristics of the structure of a supercooled liquid, glass exhibits all the mechanical properties of a solid. As in other amorphous solids, the atomic structure of a glass lacks the long-range periodicity observed in crystalline solids. Due to chemical bonding constraints, glasses do possess a high degree of short-range order with respect to local atomic polyhedra. The notion that glass flows to an appreciable extent over extended periods of time is not supported by empirical research or theoretical analysis (see viscosity in solids). Laboratory measurements of room temperature glass flow do show a motion consistent with a material viscosity on the order of 10–10 Pa s.
Health & Safety Information
- ⚠️Physical Toxicity: Quartz, silica, crystalline silica and flint are non-toxic materials, but very fine dust containing quartz, known as respirable crystalline silicon (RCS), can cause serious and fatal lung disease. Lapidaries should exercise caution when cutting silica.
Quick Facts
Physical Properties
- Color
- Various colors
- Hardness (Mohs)
- 5 - 6
- Density
- 2.4 - 2.6 g/cm³
- Luster
- Vitreous
- Crystal System
- Amorphous
Chemical Properties
- Chemical Formula
- SiO2
- Elements
- Si, O
Also Known As
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