White Engagement Rings - Not Diamonds

 Azcolvin429 at en.wikipedia

Diamonds are traditional stones of English-speaking societies. Tiffany & Co. published these poems "of unknown author" for the first time in a pamphlet in 1870.

She who from April dates her years,
Diamonds shall wear, lest bitter tears
For vain repentance flow; this stone,
Emblem of innocence, is known.

TQ Diamonds

Diamonds are a beautiful, but expensive gemstone.  Many engaged couples want that white stone.  Many cannot afford that diamond.  They can have an affordable engagement ring without buying a cubic zirconia.  Cubic zirconia (CZ) is the cubic crystalline form of zirconium dioxide (ZrO2). The synthesized material is hard, optically flawless and usually colorless.

Many natural diamonds are formed at high temperature and pressure at depths of 87 to 120 miles in the Earth's mantle. Carbon-containing minerals provide the carbon source, and the growth occurs over periods from 1 billion to 3.3 billion years (25% to 75% of the age of the Earth). Diamonds are brought close to the Earth′s surface through deep volcanic eruptions by magma. 

Polished surface of the oldest zircon
so far found on Earth - NASA

Zircon is a zirconium silicate (ZrSiO4). It is sometimes incorrectly called "cubic  zirconium". Zircon forms in silicate melts with large quantities of high field strength incompatible elements. The crystal structure of zircon is tetragonal crystal system. The natural color of zircon varies between colorless, yellow-golden, red, brown, blue, and green. Colorless samplings that show gem quality are a widespread substitute for diamond and are also known as "Matura diamond".

Rob Lavinsky, iRocks.com – CC-BY-SA-3.0

Zircon, zirconium orthosilicate, is found in most igneous rocks and some metamorphic rocks as small crystals or grains, mostly widely distributed and rarely more than 1% of the total mass of the rock. It is also found as alluvial grains in some sedimentary rocks due to its high hardness. Zircon has a high refraction index and, when the crystals are large enough, is often used as a gemstone.  

 Herkimer quartz found in NY

Rock crystal is an alternate and traditional birthstone for the month of April. Quartz is often associated with balance, clarity, and energy. It is widely used as a popular ornamental stone and is also used as a gemstone. Although it is one of the least expensive gemstones, cut rock crystal has been used as imitation diamonds. Pure quartz, traditionally called rock crystal and/or clear quartz, is colorless and transparent (clear) or translucent, Rock crystal can have the colorless clarity of pure water, unlike ordinary window glass which is a pale green.

 Sapphire is a gemstone variety of the mineral corundum, an aluminium oxide (α-Al2O3). Trace amounts of other elements such as iron, titanium, chromium, copper, or magnesium can give corundum blue, yellow, purple, orange, or a greenish color. Chromium impurities in corundum yield a pink or red tint, the latter being called a ruby. Colorless sapphires are sometimes used as diamond alternatives in jewelry. Corundum that contains ~0.01% of titanium is colorless.