Materials: Focus Crystals:

Focus Crystals are by far the most common form of Foci that wizards use due to their relative ease to grow in magically saturated areas such as leyline rifts and their intersections, their storage capacity compared to their size, and their durability to store magic being minimally diminished by the shape the focus crystals are cut into.  In addition, the multitude of colors make it easier for one to blend them into a design or at least mute the attention they draw with proper accents so as to conceal their importance.  Each color has a different capacitance and durability:

Clear: Prominent, 1 FP per cubic inch, shatters easily, 1 EP, 1 Toughness.
Light Blue: Common, 2 FP per cubic inch, slightly more resistant, 2 EP, 1 Toughness.
Dark Blue: Uncommon, 3 FP per cubic inch, slightly more resistant, 2 EP, 2 Toughness.
Light Purple: Uncommon, 2 FP per cubic inch, moderate resistance, 3 EP, 1 Toughness.
Dark Purple: Extraordinary, 3 FP per cubic inch, moderate resistance, 3 EP, 2 Toughness.
Pink: Unique, 6 FP per cubic inch, shatters easily, 1 EP, 2 Toughness.
Red: Rare, 4 FP per cubic inch, slightly more resistant, 2 EP, 3 Toughness.
Yellow: Mythical, 7 FP per cubic inch, moderate resistance, 4 EP, 2 Toughness.
Orange: Rare, 5 FP per cubic inch, higher resistance, 6 EP, 3 Toughness.
Green: Extraordinary, 4 FP per cubic inch, shatters easily, 1 EP, 7 Toughness.
Dark Green: Unique, 7 FP per cubic inch, slightly more resistant, 3 EP, 9 Toughness.
White: Fabled, 9 FP per cubic inch, incredible resistance, 9 EP, 11 Toughness.
Black: Legendary, 12 FP per cubic inch, incredible resistance, 11 EP, 9 Toughness.