When the basic ingredients of sand and minerals are heated to a high temperature and then cooled, a transparent, non-crystalline material called glass is created. This is a common occurrence in nature, where lightning or meteor strikes provide the heat that melts sand and sedimentary rock, forming glass.
Since ancient times, people have developed basic recipes for glassmaking, using native materials and hot furnaces to recreate the natural process.
Ways Glass is Formed Naturally
In nature, glass can be formed in three ways:
- When lightning strikes sand – The energy from lightning that strikes a sandy beach or sandy soil fuses natural silica glass (called lechatelierite) into fragile forms called fulgurites. These branch-like formations in the ground can range from two centimeters to three inches in diameter, and up to several feet long. The tan or grayish exterior of a fulgurite is crusty and sandy, but the interior is lined with bubbly glass. Sand fulgurites are commonly found in Florida—a state with a high number of lightning strikes—the shores of Lake Michigan, and the Atlantic coast. Fulgurites are very fragile so must be carefully excavated.
- When lightning strikes rocks – Rock fulgurites are formed when lighting strikes a rocky surface, and this commonly occurs on mountain peaks. Rather than the branch-like form of a sand fulgurite, a rock fulgurite appears as a thin, glassy crust on the rock’s surface. It has glass-lined bubbles or cavities. The glass has less silica than in sand fulgurites, and the colors are influenced by the mineral composition of the rock that was struck.
- When a meteorite collides with Earth – Another natural phenomenon that creates glass is when a meteorite strikes Earth. Parts of the outer crust are heated and suddenly cooled at impact, forming small objects, called tektites, which are scattered into enormous debris fields. They contain approximately 70 percent silica. Scientists first thought tektites, which are from 800,000 to over 64 million years old, originated from space, but now understand that they were most likely sedimentary rocks on Earth. It is interesting that tektites are found on all continents except Antarctica and South America, and their size, shape and composition vary depending on the regions in which they are found. Some tektites are located in or near large craters, others mixed in with ordinary gravel and coarse sediment.
Atomic Bomb Formed Glass
One way that glass was formed naturally but with man’s influence was through the first atomic explosion. When the nuclear bomb was detonated in New Mexico in 1945, the crater that it formed became coated with a grayish-green colored silica glass that was called “trinitite” because the test was conducted at Trinity Site. The extreme heat of the explosion had melted sand in the remote, desert location and converted it to glass.
The Basic Ingredients Man Uses to Make Glass
To make glass, people use a basic recipe of sand (silicon dioxide), soda ash (sodium carbonate) and limestone (calcium carbonate). The peoples of ancient Mesopotamia probably inadvertently made glass for the first time when they fired pottery, as the sand and minerals were fused to a glaze on their pieces. In ancient days, the mineral natron (hydrated sodium carbonate)—which was used in embalming and ceramics—was used for the soda ash.
Household baking soda (sodium bicarbonate) works just as well. The purpose of soda ash is to help the mixture melt at a lower temperature than would be required without it. While glass can be made from just sand and soda ash together, the lime controls the water content, keeping the mixture from being too fluid.
Creating Specialty Glasses
Glassmakers have discovered over time that adding various metallic oxides creates colors in the glass. When lead oxide is added, it produces the heavy glass we know as lead crystal. Over a hundred years ago, the Corning company developed heat-resistant glasses by adding borax to the basic ingredients, which resulted in the product we know as Pyrex.
More specialty glasses continue to be developed, but even in modern times, most glass is still being manufactured using the inexpensive, basic ingredients described, because its basic utility has withstood the test of time. Technology companies spend the most money researching and developing new glasses that will take the glass industry farther into the future.
Sources:
- Ellis, William S. Glass: From the First Mirror to Fiber Optics, the Story of the Substance That Changed the World. New York: Avon Books, Inc., 1998.
- “Fulgurite.” The New Encyclopedia Britannica, 15th ed., Vol. 5. Chicago: Encyclopedia Britannica, Inc., 2007.
- Rakov, Vladimir A. “Lightning Makes Glass.” 29th Annual Conference of the Glass Art Society, Tampa, Florida, 1999: The Dominick Labino Lecture. 14 May 2009 <http://plaza.ufl.edu/rakov/Gas.html>
- “Tektite.” The New Encyclopedia Britannica, 15th ed., Vol. 11. Chicago: Encyclopedia Britannica, Inc., 2007.
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