"Amphibole ( /ˈæmfɪboʊl/) is an important group of inosilicate minerals, forming prism or needlelike crystals, composed of double chain SiO
4 tetrahedra, linked at the vertices and generally containing ions of iron and/or magnesium in their structures. Amphiboles can be green, black, colorless, white, yellow, blue, or brown. The International Mineralogical Association currently classifies amphiboles as a mineral supergroup, within which are two groups and several subgroups." Mineralogy
Amphiboles crystallize into two crystal systems, monoclinic and orthorhombic. In chemical composition and general characteristics they are similar to the pyroxenes. The chief differences from pyroxenes are that (A) amphiboles contain essential hydroxyl (OH) or halogen (F, Cl) and (B) the basic structure is a double chain of tetrahedra (as opposed to the single chain structure of pyroxene). Most apparent, in hand specimens, is that amphiboles form oblique cleavage planes (at around 120 degrees), whereas pyroxenes have cleavage angles of approximately 90 degrees. Amphiboles are also specifically less dense than the corresponding pyroxenes. In optical characteristics, many amphiboles are distinguished by their stronger pleochroism and by the smaller angle of extinction (Z angle c) on the plane of symmetry. Amphiboles are the primary constituent of amphibolites. In rocks
Amphiboles are minerals of either igneous or metamorphic origin; in the former case occurring as constituents (hornblende) of igneous rocks, such as granite, diorite, andesite and others. Calcium is sometimes a constituent of naturally occurring amphiboles. Those of metamorphic origin include examples such as those developed in limestones by contact metamorphism (tremolite) and those formed by the alteration of other ferromagnesian minerals (hornblende). Pseudomorphs of amphibole after pyroxene are known as uralite. History and etymology
The name amphibole (Ancient Greek ἀμφίβολος - amphíbolos literally meaning 'double entendre', implying ambiguousness) was used by René Just Haüy to include tremolite, actinolite and hornblende. The group was so named by Haüy in allusion to the protean variety, in composition and appearance, assumed by its minerals. This term has since been applied to the whole group. Numerous sub-species and varieties are distinguished, the more important of which are tabulated below in two series. The formulae of each will be seen to be built on the general double-chain silicate formula RSi4O11.
Four of the amphibole minerals are among the minerals commonly called asbestos. These are: anthophyllite, riebeckite, cummingtonite/grunerite series, and actinolite/tremolite series. The cummingtonite/grunerite series is often termed amosite or brown asbestos; riebeckite is known as crocidolite or blue asbestos. These are generally called amphibole asbestos. Mining, manufacture and prolonged use of these minerals can cause serious illnesses."
There are currently 118 known chemical elements exhibiting a large number of different physical and chemical properties. Amongst this diversity, scientists have found it useful to use names for various sets of elements, that illustrate similar properties, or their trends of properties. Many of these sets are formally recognized by the standards body IUPAC.
The following collective names are recommended by IUPAC: Alkali metals – The metals of group 1:
Li,
Na,
K,
Rb,
Cs,
Fr. Alkaline earth metals – The metals of group 2:
Be,
Mg,
Ca,
Sr,
Ba,
Ra. Pnictogens – The elements of group 15:
N,
P,
As,
Sb,
Bi.
(Mc
had not yet been named when the 2005 IUPAC Red Book was published, and its chemical properties are not yet experimentally known.) Chalcogens – The elements of group 16:
O,
S,
Se,
Te,
Po.
(Lv
had not yet been named when the 2005 IUPAC Red Book was published, and its chemical properties are not yet experimentally known.) Halogens – The elements of group 17:
F,
Cl,
Br,
I,
At.
(Ts had not yet been named when the 2005 IUPAC Red Book was published, and its chemical properties are not yet experimentally known.) Noble gases – The elements of group 18:
He,
Ne,
Ar,
Kr,
Xe,
Rn.
(Og had not yet been named when the 2005 IUPAC Red Book was published, and its chemical properties are not yet experimentally known.) Lanthanoids – Elements 57–71:
La,
Ce,
Pr,
Nd,
Pm,
Sm,
Eu,
Gd,
Tb,
Dy,
Ho,
Er,
Tm,
Yb,
Lu, Actinoids – Elements 89–103:
Ac,
Th,
Pa,
U,
Np,
Pu,
Am,
Cm,
Bk,
Cf,
Es,
Fm,
Md,
No,
Lr. Rare-earth metals –
ScY, plus the
lanthanoids Transition elements – Elements in groups 3 to 11 or 3 to 12.
