Metallic Crystals of Bismuth Grown in the Lab
Hopper Crystals are artificially grown crystals, grown either in the lab or at home, mainly for collectors and gem shops. The name "Hopper Crystals" gets its name from the unlikely source of a type of "hopper cart" familiar to farms and in agricultural use. A hopper cart is a wagon with high sides and steep interior angles that direct loose contents downwards towards a trap door at the bottom, which is opened for rapid unloading. Railway cars that carry grain, coal, gravel or sand or other heavy bulk materials use the "hopper cart" design.
During a recent visit to a gem and crystal shoppe here in the east end of Toronto, Canada, I bought some interesting specimens including several walnut-sized crystals of lab-grown bismuth. The pastel iridescence and unusual crystal lattices are what intrigued me. All of the images used in this article are of the specimen that I purchased.
I was only vaguely aware what 'hopper crystals' are and this article is written from what I have learned.
What are "Hopper Crystals?"
In crystallography, forcibly growing crystals of certain elements and molecular compounds rapidly causes them to form the beautiful but unnatural "hopper crystals." In nature, hopper crystals would not normally occur unless there are extenuating circumstances.
In the forced and accelerated growth in the lab however, hopper crystals are predictably created. As in nature, each one being unique and different. No two are ever exactly alike.
In the formation of hopper crystals, there is a minute electrical attraction in the molecules which is greater along the outer edges of the growing crystal and causes faster growth there than at the interior edge, which grows slightly slower. This causes unnatural angular crystals to form.
Bismuth is the last naturally-occurring stable and non-radioactive element on the Periodic Table of Elements, even though it is in fact very slightly radioactive....
More molecules are drawn into the outer edge of the growing crystal than the inner edge, forming the "hopper cart" shape. This characteristic is known to occur in a number of minerals and elements such as calcite, halite, gold, and even in water (in the form of ice, and snowflakes!) and of course, what we are discussing here; the heavy inert metallic element bismuth.
What is Bismuth?
Bismuth is said to be the last naturally-occurring stable and non-radioactive element on the Periodic Table of Elements, even though it is in fact very slightly radioactive.
Uses for Bismuth are many which include lead substitutes, certain medicinal preparations (such as Pepto-Bismol, which contains Bismuth subsalicylate.) Bismuth is used in some cosmetics for the color oxidized bismuth has, and as in ingredient in metal solder mainly for its swelling (increasing in size) as it cools from the molten to solidified state. This makes it ideal for using as an additive to solder welding.
There is even research into using bismuth as a possible replacement for Xenon in a type of rocket thruster engine. Under certain conditions, bismuth acts as a semi-conductor and its possible use in electronics circuitry is being investigated as well.
(Above: Looking like an ancient Mayan Pyramid, the 'Hopper Effect' of crystallization is very apparent in this lab-grown Bismuth crystal)
Its low melting point makes it useful for passive/automatic fire suppression devices whereby the heat of uncontrolled fire causes it to melt, triggering or releasing whatever fire-suppressing mechanism is used (chemical powder, water, carbon dioxide, etc.) These could be sprinklers in apartment building, fire-suppression hoods in restaurant kitchens, perhaps automatic fire-suppression on race car engines under the hood (veracity unknown: speculation on my part,) and most gasoline/petrol stations have a fire-suppression system over the filling pumps that probably employs not only a manual suppression ability but a passive (automatic) heat-activated release system using bismuth as well.
Extreme Close-up of a Bismuth Crystal
(Left: Extreme close-up of a Bismuth crystal exhibiting the Hopper Crystal effect)
It is notable that its use as a substitute for the element lead is making bismuth an increasing valuable commodity. In sports hunting, the pellets used in shot shell for hunting waterfowl are no longer made from toxic lead, but from bismuth.
The unrecoverable lead pellets from shot shells are often mistakenly ingested by waterfowl that require ‘grit’ in their gizzards to digest their food.
These spent pellets that fall back to the ground and wetlands are also eaten by turtles, frogs and other animals that presumably mistake these little round beads of lead for food.
Ingesting lead shot pellets over the long term causes them to suffer from health problems related to lead poisoning. Bismuth does not have this risk and is deemed to be far safer than lead in regards to accidental or incidental ingestion.
As a bismuth crystal oxidizes it forms iridescent rainbow colors on the exterior lattices, colors which are so mesmerizing to view. I find myself quite bemused with these pastel colors and bizarre shapes.
(All images by author)