Hydrogrossular, is a calcium

Calcium

Calcium is the chemical element with the symbol Ca and atomic number 20. It has an atomic mass of 40.078 amu. Calcium is a soft gray alkaline earth metal, and is the fifth-most-abundant element by mass in the Earth's crust...

 aluminium

Aluminium

Aluminium or aluminum is a silvery white member of the boron group of chemical elements. It has the symbol Al, and its atomic number is 13. It is not soluble in water under normal circumstances....

 garnet

Garnet

The garnet group includes a group of minerals that have been used since the Bronze Age as gemstones and abrasives. The name "garnet" may come from either the Middle English word gernet meaning 'dark red', or the Latin granatus , possibly a reference to the Punica granatum , a plant with red seeds...

 series (formula: Ca₃Al₂(SiO₄)_3-x(OH)_4x, with hydroxide (OH) partially replacing silica (SiO₄)). The endmembers of the hydrogarnet family (grossular

Grossular

Grossular or grossularite is a calcium-aluminium mineral species of the garnet group with the formula Ca3Al23, though the calcium may in part be replaced by ferrous iron and the aluminium by ferric iron. The name grossular is derived from the botanical name for the gooseberry, grossularia, in...

, hibschite, and katoite) depend on the degree of substitution (x):

• grossular: x = 0
• hibschite: 0.2 < x < 1.5
• katoite: 1.5 < x < 3.

Hydrogrossular is a garnet variety in which a Si⁴⁺ is missing from a tetrahedral site. Charge balance is maintained by bonding a H⁺ to each of the four oxygens surrounding the vacant site.

Hydrogrossular is found in massive crystal habit

Crystal habit

Crystal habit is an overall description of the visible external shape of a mineral. This description can apply to an individual crystal or an assembly of crystals or aggregates....

, sometimes grown in with idocrase.

Hydrogrossular is translucent to opaque

Opacity (optics)

Opacity is the measure of impenetrability to electromagnetic or other kinds of radiation, especially visible light. In radiative transfer, it describes the absorption and scattering of radiation in a medium, such as a plasma, dielectric, shielding material, glass, etc...

, and found in green to bluish green, pink, white, and gray. The cause of the green color is chromium

Chromium

Chromium is a chemical element which has the symbol Cr and atomic number 24. It is the first element in Group 6. It is a steely-gray, lustrous, hard metal that takes a high polish and has a high melting point. It is also odorless, tasteless, and malleable...

, and possibly iron

Iron

Iron is a chemical element with the symbol Fe and atomic number 26. It is a metal in the first transition series. It is the most common element forming the planet Earth as a whole, forming much of Earth's outer and inner core. It is the fourth most common element in the Earth's crust...

. Pink hydrogrossular is caused by the presence of manganese

Manganese

Manganese is a chemical element, designated by the symbol Mn. It has the atomic number 25. It is found as a free element in nature , and in many minerals...

. Hydrogrossular may have dark gray to black small inclusions. It has similarities to jade

Jade

Jade is an ornamental stone.The term jade is applied to two different metamorphic rocks that are made up of different silicate minerals:...

, and has the misnomer

Misnomer

A misnomer is a term which suggests an interpretation that is known to be untrue. Such incorrect terms sometimes derive their names because of the form, action, or origin of the subject becoming named popularly or widely referenced—long before their true natures were known.- Sources of misnomers...

s Transvaal jade, and African jade.

Hydrogrossular is sometimes used as a gemstone

Gemstone

A gemstone or gem is a piece of mineral, which, in cut and polished form, is used to make jewelry or other adornments...

, being cabochon

Cabochon

A cabochon , from the Middle French caboche , is a gemstone which has been shaped and polished as opposed to faceted. The resulting form is usually a convex top with a flat bottom. Cutting en cabochon is usually applied to opaque gems, while faceting is usually applied to transparent stones...

 cut, or made into bead

Bead

A bead is a small, decorative object that is usually pierced for threading or stringing. Beads range in size from under to over in diameter. A pair of beads made from Nassarius sea snail shells, approximately 100,000 years old, are thought to be the earliest known examples of jewellery. Beadwork...

s. Sources for green and pink hydrogrossular are South Africa

South Africa

The Republic of South Africa is a country in southern Africa. Located at the southern tip of Africa, it is divided into nine provinces, with of coastline on the Atlantic and Indian oceans...

, Canada

Canada

Canada is a North American country consisting of ten provinces and three territories. Located in the northern part of the continent, it extends from the Atlantic Ocean in the east to the Pacific Ocean in the west, and northward into the Arctic Ocean...

, and the US. White hydrogrossular is sourced from Burma and China

China

Chinese civilization may refer to:* China for more general discussion of the country.* Chinese culture* Greater China, the transnational community of ethnic Chinese.* History of China* Sinosphere, the area historically affected by Chinese culture...

.