The phrase "a crystal was" is correct and usable in written English.
It can be used in contexts where you are describing an event or situation involving a crystal, such as in scientific writing or storytelling.
Example: "A crystal was found in the cave, sparkling under the dim light."
Alternatives: "a crystal existed" or "a crystal appeared".
Prior to Shechtman's discovery, the definition of a crystal was a material in which atoms are arranged in a regular pattern that repeats itself.
With a view to determine whether the yellow form was photochromic in the solid state, a crystal was crushed on a filter paper with the intention then of irradiating the expected yellow powder with ultraviolet light.
On Bob's machine, the magnet was so strong that the moment a crystal was put on, the force that attracted the cap on the machine shook the crystal off from the nylon loop, no matter how careful I was.
In the 19th century, a complete catalog of the possible symmetries of a crystal was worked out by Johan Hessel, Auguste Bravais, Evgraf Fedorov, Arthur Schönflies and (belatedly) William Barlow.
Prior to data collection, a crystal was flash-frozen in liquid nitrogen.
After optimization in manual trays, a crystal was obtained in 3 M (NH4 2SO4, 1% (v/v) MPD, and harvested and flash-frozen in 3 M AmSO4, 1% (v/v) MPD, 25% (v/v) glycerol.
To a mathematician, a crystal is a regular system of points that, if repeated indefinitely, will fill all of space.
Over time, uranium decays into lead; the older a crystal is, the greater the fraction of lead it contains.
In homoepitaxy a crystal is grown on a substrate of the same material.
A crystal is a well-ordered arrangement of atoms that can best be pictured as spheres touching one another.
The thermoelastic stress within a crystal is calculated based on the crystal temperature.
