Zinc (Zn) is brittle, but it becomes malleable at 100° C.  Zinc, a blue-gray, metallic element, is a moderately good conductor of electricity.  The most common alloy is brass, which is a mixture of zinc and copper.


Tungsten (W) is a gray-white metallic element that is stable and is very resistant to acids and bases. Tungsten has the highest melting temperature of any metal (3422°C or 6192°F), and the second highest of all elements (carbon is highest).


Tantalum (Ta) has a very high melting point (2996°C), exceeded only by that of carbon, tungsten, and rhenium, and is remarkably resistant to attack by air, water and most acids.  Tantalum is a hard, grayish-blue, metallic element.


Sulfur (S) is a bright, lemon yellow, soft, non-metallic element that has a very low thermal conductivity, meaning it cannot transfer heat very well. The touch of a hand will cause a sulfur crystal to crack because the crystal’s surface warms faster than the interior. Sulfur melts at 108 degrees Celsius. Sulfur means “burning stone” in reference to its source from volcanoes and that it burns so easily. When sulfur is burned it combines with oxygen producing sulfur dioxide, SO2, which has a sharp pungent smell.


Strontium (Sr) is the 15th most abundant element in the earth’s crust. Only two minerals, however—celestite and strontianite—contain strontium in sufficient quantities to make recovery practical, and these minerals are found predominantly in sedimentary rocks. Strontium is a silvery-yellow, metallic element. Strontium belongs to a group of elements known as the alkali earth metals. Like other alkali metals, it is chemically active and will react with both air and water.


Silver (Ag) has a bright, metallic luster, and when untarnished, has a white color. It is rarely found in its native form. Silver can be found combined with a number of different elements such as sulfur, arsenic, antimony or chlorine to form a variety of minerals and ores, such as argentite, chlorargyrite, and galena. It is also found in very small amounts in gold, lead, zinc and copper ores. Silver is malleable which means it can be hammered into thin sheets. It is also ductile, meaning it can be drawn into wire.


Rubidium (Rb) is a very soft, silvery-white metallic element. Rubidium does not combine with other elements or ions to create minerals.

Like other alkali metals, rubidium reacts violently with air and water. When exposed to air, it bursts into flame, and explodes when put in water. Its melting point is so low (103 degrees F, 40 degrees C) that it will melt on a very hot day.

One isotope of rubidium is radioactive. Because it is impossible to separate this isotope from non-radioactive rubidium, nearly all processed rubidium is slightly radioactive.


Rhenium (element #75, symbol Re) is a rare, silvery-white metallic element.  Rhenium is found as a trace element in platinum ores and in the mineral columbite.  It is very dense and has a melting temperature of 3186 degrees C (5767 degrees F).  Rhenium does not form minerals of its own, but does occur as a trace element in the minerals columbite, tantalite and molybdenite.

Rare Earths

The rare earths, or rare earth elements (REE), are a relatively abundant group of elements consisting of scandium, yttrium, and the 15 elements of the lanthanide series of the periodic table.

Scandium (Sc) is the lightest rare earth element.  Scandium is present in crustal rocks in amounts greater than lead and precious metals, but it rarely occurs in concentrated quantities because it does not combine into common ores or minerals.

Yttrium (Y) is chemically similar to the lanthanides and often occurs with other rare earths in the same minerals as a result of its similar ionic radius.

The lanthanides consist of 15 elements with atomic numbers 57 through 71.  They are lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb) and lutetium (Lu).

Monazite is one of the most common minerals of rare earth elements.


Potassium is mined as potash, which is any salt, mined or manufactured, which contains the element potassium (K) in water-soluble form. Primary potash minerals include potassium chloride (KCl or sylvite), potassium sulfate [K2SO4, usually a manufactured product], and potassium-magnesium sulfate [K2SO4•2MgSO4 or langbeinite]. The name derives from pot ash, which refers to plant ashes soaked in water in a pot, the primary means of manufacturing the product before the industrial era. The word potassium is derived from potash.