# 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 H$_2$ at cryogenic temperatures and pressures, including room pressure or atmospheric pressure.
Solid hydrogen (H$_2$) 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
    X$_2$Y$_5$Z$_8$O$_{22}$(OH)$_2$ where
    X is magnesium, ferrous iron (Fe$^{2+}$), calcium, lithium, sodium, and ferric iron (Fe$^{3+}$)
    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 (KLi $_2$Al(Al,Si) $_3$O $_{10}$(F,OH) $_2$ 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 Li$_3$PO$_4$, with 37.5 at % lithium.

## Micas

Def. a group of monoclinic phyllosilicates with the general formula
    X$_2$Y$_{4–6}$Z$_8$O$_{20}$(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 Fe$^{3+}$ 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 (Na,Ca) $_2$Ta $_2$O $_6$(O,OH,F). 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)$_2$O$_6$, where
    X is calcium, sodium, ferrous iron (Fe$^{2+}$), magnesium, zinc, manganese and lithium;
    Y is chromium, aluminum, ferric iron (Fe$^{3+}$), magnesium, manganese, scandium, titanium, vanadium, and ferrous iron (Fe$^{2+}$)
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)$_2$O$_6$ (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

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