Calcium Amphibole Subgroup

The calcium amphibole subgroup contains the most common amphiboles. Most of the undefined “hornblende” specimens belong in this group, and the most common amphibole compositions are in the actinolite/tremolite - magnesio-hornblende - pargasite range. Some of the more common amphiboles produce large, well-formed crystals, that might even be considered attractive display specimens. Minerals in this subgroup are widespread in both metamorphic and igneous rocks, they are generally more ferric in the igneous rocks, but despite many attempts no universal correlation between bulk rock chemistry and amphibole composition has been established. There is a significant overlap between the different minerals in both geochemistry and PT conditions, and often, several species are found at the same localities. The minerals in this group are notoriously difficult to identify for collectors, and therefore often not identified or reported. For further information, see https://www.mindat.org/article.php/3937/Calcium+Amphibole+Subgroup

History

Activities related to discovery and approval of the group members

Structural context

Monoclinic System
314 measurement(s) or 100.00%78 member(s) or 85.71%
Unclassified
0 measurement(s) or 0.00%13 member(s) or 14.29%
a9.64—10.032 (9.86)
b17.79999—18.296 (18.0592)
c5.228—5.372 (5.2928)
alpha90
beta73.97—105.95 (104.4898)
gamma90
volume870.488—945.663 (910.7833)

Based on 314 measurements
Actinolite
Actinolite-Ferro-actinolite Series
Actinolite-Tremolite Series
Alkali-femaghastingsite
Alkali-ferrohastingsite
Chrome-Tremolite
Chromio-pargasite
Edenite
Femaghastingsite
Ferri-cannilloite
Ferri-fluoro-cannilloite
Ferri-fluoro-sadanagaite
Ferri-fluoro-tschermakite
Ferri-sadanagaite
Ferri-tschermakite
Ferro-actinolite
Ferro-cannilloite
Ferro-chloro-pargasite
Ferro-edenite
Ferro-ferri-cannilloite
Ferro-ferri-fluoro-cannilloite
Ferro-ferri-fluoro-hornblende
Ferro-ferri-fluoro-sadanagaite
Ferro-ferri-fluoro-tschermakite
Ferro-ferri-hornblende
Ferro-ferri-sadanagaite
Ferro-ferri-tschermakite
Ferro-fluoro-actinolite
Ferro-fluoro-cannilloite
Ferro-fluoro-edenite
Ferro-fluoro-hornblende
Ferro-fluoro-pargasite
Ferro-fluoro-sadanagaite
Ferro-fluoro-tschermakite
Ferro-hornblende
Ferro-pargasite
Ferro-sadanagaite
Ferro-tschermakite
Fluoro-cannilloite
Fluoro-edenite
Fluoro-hastingsite
Fluoro-pargasite
Fluoro-sadanagaite
Fluoro-tremolite
Fluoro-tschermakite
Hastingsite
Hexagonite
Joesmithite
Magnesio-ferri-fluoro-hornblende
Magnesio-ferri-hornblende
Magnesio-fluoro-hastingsite
Magnesio-fluoro-hornblende
Magnesio-hastingsite
Magnesio-hornblende
Pargasite
Parvo-mangano-edenite
Parvo-manganotremolite
Philipstadite
Potassic-chloro-hastingsite
Potassic-chloro-pargasite
Potassic-chloro-sadanagaite
Potassic-ferro-chloro-edenite
Potassic-ferro-chloro-sadanagaite
Potassic-ferro-ferri-sadanagaite
Potassic-ferro-pargasite
Potassic-ferro-sadanagaite
Potassic-fluoro-hastingsite
Potassic-fluoro-pargasite
Potassic-hastingsite
Potassic-magnesio-hastingsite
Potassic-pargasite
Potassic-sadanagaite
Sadanagaite
Smaragdite
Tremolite
Tremolite-Actinolite Series
Tschermakite
Vanadio-pargasite

Chemical context

Stoichiometric formulas

Calcium Amphibole Subgroup
mindat.org
  • March 13, 2023AnCa2(Z2+5-mZ3+m)(Si8-(n+m)Al(n+m))(OH,F,Cl)2The calcium amphibole subgroup is one of the subgroups belonging to the W(OH,F,Cl)amphibole group. It is defined by Ca>1,5 apfu in the X position (= IMA B position). The calcium amphibole subgroup are further divided into root-name groups that are defined by the value of n and m (edenite and tschermakite substitutions) in the generic formula above. The generic formula does not apply fully to root-name groups or species containing elements with other valence values than standard. The various positions in the formula can have the following content: A position: x=0 or 1, when 1, it normally contains a single valence element,most often Na or K but also Ca or Pb. Z2+ position (= IMA C2+ position): m may be 0,1 or 2. The Z2+ positions normally contains Mg or Fe as the dominant elements. Z3+ position (= IMA C3+ position): Normally contains Al or Fe, but also Cr or Ti are known as the dominant elements in this position. On mindat.org we avoid using variables with the same symbol as elements and deviate from the IMA nomenclaure in that we use X rather than B, Z rather than C and (OH,F,Cl,O) rather than W.
mineralogy.rocks
  • Aug. 30, 2022AB2C5(X8O22)Z2

Elements recorded on EPMA

291
Ca
290
O
288
Mg
288
Si
267
Na
264
Al
253
H
248
Fe
218
K
190
Ti
169
Mn
118
Cr
95
F
38
Cl
7
Ga
6
Zn
3
V
2
Ba
2
I
2
Pb
2
Sc
1
B
1
Be
1
Li
1
Ni
1
Sr

Physical properties

ColorColor entities, recognized using a custom trained NER model
26
  • brownish black
  • brownish-black
  • dark greenish black
  • green-black
  • greenish black
  • grey-black
22
  • black-green
  • bright green
  • brownish-green
  • dark green
  • dark-green
  • dark greenish
  • emerald green
  • grey-green
  • light green
  • light-greenish
14
  • brownish
  • dark brown
  • green-brown
  • greenish-brown
  • light-brown
  • pale pinkish-brown
3
  • light yellow
3
  • colourless
  • pale
2
    2
      1
      • pink-violet
      Color noteOriginal color note from the source
      Black; Black, dark brown; Black, dark green; Black, dark-green, greenish-brown, yellow; Black-green, dark green; Bright green to emerald green; Brownish black; Brownish-black; Dark brown to black; Dark greenish; Dark greenish black; Dark green to black, greenish-brown, more rarely lighter green; Emerald green; Emerald green to pale green; Green; Green-brown, black; Green, brownish, black; Green, green-black, grey-green, or black; Greenish black; Greenish-brown to dark green, black.; Green to brownish-green; Grey-green; Light-brown, brown, greenish-brown to dark green and black.; Light-greenish to colourless; Light green to light yellow, grey-black; Medium green to dark green to green-black to black, also brownish-green.; Medium green to dark green to green-black to black, brown; Medium green to dark green to green-black to black, brown (rare).; Very pale pinkish-brown; White, brown, colourless, grey, light green, green, light yellow, pink-violet; White, grey, pale to dark green, also brown and pale pinkish-brown
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      StreakStreak entities, recognized using a custom trained NER model
      11
      • brownish green
      • dark green
      • pale green
      • pale grey-green
      11
      • greenish white
      • grey-white
      7
      • gray
      • greenish grey
      • pale grey
      • pale-grey
      4
      • pale brown
      Streak noteOriginal streak note from the source
      Brownish green; Dark green; Gray; Greenish grey; Greenish white; Green, pale grey; Grey to greenish grey; Grey-white; Grey-white, yellowish white; Pale brown; Pale green; Pale-grey; Pale grey-green; Pale grey-green, grey-white; Pale grey-green to brownish-green; Pale grey-green to brownish-green.; Pale grey-green to pale brownish-green; White
      Lustre
      • Silky2
      • Vitreous37
      • Sub-Adamantine1
      • Sub-Vitreous1
      Fracture
      • Irregular/Uneven4
      • Splintery3
      • Sub-Conchoidal1
      • Conchoidal5
      Transparency
      • Opaque3
      • Transparent10
      • Translucent11
      Luminescence
      Non-fluorescent; Nonfluorescent
      Tenacity
      • brittle15
      Hardness