Step 1: Introduction to Gemology

Lesson 5

Since the principal source of ingredients for gems is the rocky Earth itself, knowing the abundance of the elements that make up the minerals in the Earth’s crust will help us understand why there are common and uncommon gemstones.

The Abundance of Elements in the Earth’s Crust

The following figures are estimated percentages of the Earth’s crust by weight.

The eight most common elements in the crust are:

  • Oxygen (O) 46.4%
  • Silicon (Si) 28.15%
  • Aluminum (Al) 8.23%
  • Iron (Fe) 5.63%
  • Calcium (Ca) 4.15%
  • Sodium (Na) 2.36%
  • Magnesium (Mg) 2.33%
  • Potassium (K) 2.09%

All other elements represent a mere 0.66% of the crust.

From a gemological perspective, the following uncommon elements in the Earth’s crust are of particular interest:

  • Manganese (Mn) 0.095%
  • Carbon (C) 0.02%
  • Zirconium (Zr) 0.0165%
  • Vanadium (V) 0.0135%
  • Chromium (Cr) 0.01%
  • Nickel (Ni) 0.0075%
  • Copper (Cu) 0.0055%
  • Cobalt (Co) 0.0025%
  • Lithium (Li) 0.002%
  • Beryllium (Be) 0.00028%

A World of Oxygen and Silicon

Oxygen and silicon make up more than 74% of the Earth’s crust. It’s not surprising that quartz (SiO2) is one of the most common gemstone minerals.

However, oxygen and silicon are also found in…