Minerals/Metals/Alkalis

The alkalis, or alkali metals, are the group 1 elements of the Periodic Table. In addition to the true metals: lithium (Li), sodium (Na), potassium (K), rubidium (Rb), caesium (Cs), and francium (Fr), hydrogen (H) is usually included.

Each of the elements in group 1 has or may have native mineral occurrences on Earth or elsewhere nearby.

Hydrogens
Native hydrogen is not known to occur on the surface of the Earth. As the pressure-temperature phase (PTP) diagram for hydrogen on the left suggests there can be solid metallic monatomic hydrogen and solid H2 at cryogenic temperatures and pressures, including room pressure or atmospheric pressure.

Solid hydrogen (H2) occurs in a hcp structure transitioning to a broken symmetry phase (BSP), then to the A phase at atmospheric pressure with increasing temperature.

Lithiums
As indicated in the magnesium-lithium phase diagram on the left, lithium occurs in the same crystal structure at lower temperatures as it does up to melting temperature. This is the bcc phase (α-Li).

"Native lithium is rare in nature. Most of the lithium is extracted from the mining [of] spodumene."

Amphiboles
Def. a group of monoclinic or orthorhombic double chain inosilicates with the general formula of
 * X2Y5Z8O22(OH)2 where
 * X is magnesium, ferrous iron (Fe2+), calcium, lithium, sodium, and ferric iron (Fe3+)
 * Y is Al, Mg, or Fe or less commonly Mn, Cr, Ti, Li, etc.
 * Z is chiefly Si or Al

is called an amphibole.

"We take the boundary between the lithium and calcium, and lithium and magnesium–iron–manganese amphiboles at Li: Ca and Li: (Mg + Fe + Mn) ratios of 0.50 (ie, we use the criterion of the dominant cation or, in the case of the magnesium–iron–manganese amphiboles, the dominant group of cations) in both SCHEME 1 and SCHEME 2."

Lepidolites
Lepidolite ( is a lilac-gray or rose-colored member of the mica group that is a secondary source of lithium, a phyllosilicate mineral and a member of the polylithionite-trilithionite series.

It is associated with other lithium-bearing minerals like spodumene in pegmatite bodies. It is one of the major sources of the rare alkali metals rubidium and caesium.

It occurs in granite pegmatites, in some high-temperature quartz veins, greisens and granites. Associated minerals include quartz, feldspar, spodumene, amblygonite, tourmaline, columbite, cassiterite, topaz and beryl.

Lithiophosphates
Lithiophosphate has the chemical formula Li3PO4, with 37.5 at % lithium.

Micas
Def. a group of monoclinic phyllosilicates with the general formula
 * X2Y4–6Z8O20(OH,F)4
 * in which X is K, Na, or Ca or less commonly Ba, Rb, or Cs;
 * Y is Al, Mg, or Fe or less commonly Mn, Cr, Ti, Li, etc.;
 * Z is chiefly Si or Al, but also may include Fe3+ or Ti;
 * dioctahedral (Y = 4) and trioctahedral (Y = 6)

is called a mica.

Microlites
Microlite is composed of sodium calcium tantalum oxide with a small amount of fluorine. Microlite is a mineral in the pyrochlore group that occurs in pegmatites and constitutes an ore of tantalum. It has a Mohs hardness of 5.5 and a variable specific gravity of 4.2 to 6.4. It occurs as disseminated microscopic subtranslucent to opaque octahedral crystals with a refractive index of 2.0 to 2.2. Microlite is also called djalmaite. Microlite occurs as a primary mineral in lithium-bearing granite pegmatites, and in miarolitic cavities in granites.

Pyroxenes
Def. a group of monoclinic or orthorhombic, single chain inosilicates with the general formula of X Y(Si,Al)2O6, where
 * X is calcium, sodium, ferrous iron (Fe2+), magnesium, zinc, manganese and lithium;
 * Y is chromium, aluminum, ferric iron (Fe3+), magnesium, manganese, scandium, titanium, vanadium, and ferrous iron (Fe2+)

is called a pyroxene.

The pyroxenes are a group of important rock-forming inosilicate minerals found in many igneous and metamorphic rocks. They share a common structure consisting of single chains of silica tetrahedra and they crystallize in the monoclinic and orthorhombic systems. Pyroxenes have the general formula XY(Si,Al)2O6 (where X represents calcium, sodium, iron+2 and magnesium and more rarely zinc, manganese and lithium and Y represents ions of smaller size, such as chromium, aluminium, iron+3, magnesium, manganese, scandium, titanium, vanadium and even iron+2). Although aluminium substitutes extensively for silicon in silicates such as feldspars and amphiboles, the substitution occurs only to a limited extent in most pyroxenes.

At right is an image of a very rare, sharp, complete-all-around pyroxene is from Ducktown District, Polk County, Tennessee, USA, circa mid to late 1800s.

Sodiums
The phase diagram on the left shows bcc (α-Na) at higher temperatures up to melting and hcp (β-Na) with decreasing temperature below the transition at 97.8°C.

Native sodium does not appear to occur on the surface of the Earth.

Halites
Halite (NaCl) is probably the most common mineral containing sodium at 50 at %. It is a cubic mineral usually found in arid locations on Earth. Occurrences have clear, white, purple, blue, yellow, orange, and red varieties.

Villiaumites
Villiaumite has the chemical formula NaF, with 50 at % sodium.

Potassiums
As indicated in the phase diagram on the left, potassium occurs in a bcc (α-K) phase from room temperature up to melting.

Native potassium does not appear to occur on the Earth's surface.

Rubidiums
The pressure-temperature diagram on the left shows that rubidium is bcc (α-Rb) from room temperature through melting.

Native rubidium does not appear to occur on the Earth's surface.

Caesiums
As the temperature-pressure diagram on the left shows, caesium (formerly cesium) is bcc (α-Cs) from room temperature up to melting.

Native caesium does not appear to occur on the surface of the Earth or the Moon.

Franciums
Francium is bcc at room temperature.

Hypotheses

 * 1) Alkalis, or alkali metals, are the most reactive metals in the Periodic Table.