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This is an outstanding piece of spodumene because it has a real termination that is sharp, uncommon for the county, and it has intense color. Credit: Robert M. Lavinsky.{{free media}}

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.


This is a proposed or tentative phase diagram for hydrogen with temperature and pressure. Credit: Isaac Silvera.

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.


This is a magnesium-lithium phase diagram. Credit: T. Massalski, H. Okamoto, P. Subramanian, L. Kacprzak, ASM International.

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."[1]


This image shows several amphibole crystals in a glass bowl. Credit: Karelj.

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."[2]


Lavender lepidolite has been found in the Himalaya Mine, Mesa Grande District, San Diego County, California, USA. Credit: Rob Lavinsky.

Lepidolite (KLi2Al(Al,Si)3O10(F,OH)2 is a lilac-gray or rose-colored member of the mica group that is a secondary source of lithium. It is a phyllosilicate mineral[3] and a member of the polylithionite-trilithionite series.[4]

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.[5]

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.


Lithiophosphate has the chemical formula Li3PO4, with 37.5 at % lithium.[6]


Here is mica in a rock. Credit: Rpervinking.

Def. a group of monoclinic phyllosilicates with the general formula[7]

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.


The image shows pale-yellow microlite on lepidolite. Credit: Rob Lavinsky.

Microlite is composed of sodium calcium tantalum oxide with a small amount of fluorine (Na,Ca)2Ta2O6(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.


This very rare, sharp, complete-all-around pyroxene is circa mid to late 1800s. Credit: Robert Lavinsky.

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.


This is a phase diagram for the sodium-bismuth system. Credit: J. Sangster and A.D. Pelton.

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.


This is a sodium chloride crystal of the mineral halite. Credit: United States Geological Survey and the Mineral Information Institute.

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.[6]


Villiaumite has the chemical formula NaF, with 50 at % sodium.[6]


This is a pressure-temperature phase diagram for potassium. Credit: David A. Young, ERDA.

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.


This is a pressure-temperature phase diagram for rubidium. Credit: David A. Young, ERDA.

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.


Temperature-pressure diagram for caesium, formerly known as "cesium". Credit: David A. Young, ERDA.

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.


Francium is bcc at room temperature.


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

See also[edit]


  1. Shanghai Xuanshi Machinery Co., Ltd. (2011). "Xuanshi". Shanghai, PRC: Shanghai Xuanshi Machinery Co., Ltd. Retrieved 2015-08-22.
  2. Frank C. Hawthorne and Roberta Oberti (2006). "On the classification of amphiboles". The Canadian Mineralogist. 44 (1): 1–21. doi:10.2113/gscanmin.44.1.1. Retrieved 2011-11-21. Unknown parameter |month= ignored (help)
  3. Hurlbut, Cornelius S.; Klein, Cornelis (1985). Manual of Mineralogy, Wiley, (20th edition ed.). ISBN 0-471-80580-7
  4. Lepidolite on Mindat.org
  5. H. Nechamkin, The Chemistry of the Elements, McGraw-Hill, New York, 1968.
  6. 6.0 6.1 6.2 Willard Lincoln Roberts, George Robert Rapp, Jr., and Julius Weber (1974). Encyclopedia of Minerals. 450 West 33rd Street, New York, New York 10001 USA: Van Nostrand Reinhold Company. p. 693. ISBN 0-442-26820-3. |access-date= requires |url= (help)CS1 maint: multiple names: authors list (link) CS1 maint: location (link)
  7. Deer, W. A., R. A. Howie and J. Zussman (1966) An Introduction to the Rock Forming Minerals, Longman, ISBN 0-582-44210-9

External links[edit]