Petrographic Description

Petrographic Description

Identification
    Description ID: Sample
    Thin section ID: 17a
    Rock type: Igneous
    Well/Outcrop name: SampleWell
    Top depth: 3189.0
    Unit/Age: Lower Cretaceous
    Block/Province: Sample
    Country: Brazil
    State: XX
    Place: Nativo
    Institution: Endeeper
    Petrographer: De Ros
    First edition date: Oct 4, 2010
    Last edition date: Apr 6, 2011
    Uses: Stratigraphic, Exploration

Summary
    Dolerite (diabase) constituted of calcic plagioclase and augite, in intergranular arrangement. Intersertal spaces originally occupied by glass, are presently crystallized partially to divergent aggregates of albite in variolitic texture. Abundant skeletal ilmenite in symplectitic intergrowth with the pyroxene and the plagioclase. Subordinate olivine crystals, presently replaced by iddingsite and serpentine. Incipient alteration and fracture filling by calcite and smectite (nontronite).

Macroscopic features

    Structure(s): Massive, Vein
    Color(s): Grayish green (10 GY 5/2)
   Granularity: Aphanitic

   Description: Nst1ES 3189 intergr 2,5
   Subtitle:
          P: Constituent name: Plagioclase;
          A: Constituent name: Augite;
          I: Constituent name: Ilmenite;
   Purposes: Texture

   Description: Nst1ES 3189 ilmenita 5
   Subtitle:
          I: Constituent name: Ilmenite;
          Pl: Constituent name: Plagioclase;
          Ag: Constituent name: Augite;
          Gl: Constituent name: Mafic glass;
   Purposes: Primary composition, Primary habit

   Description: Nst1ES 3189 interser 2,5
   Subtitle:
          Dark blue Arrow: Constituent name: Albite - Paragenetic relation: Replacing <Constituent> - Paragenetic relation constituent: Mafic glass;
   Purposes: Texture, Primary composition

   Description: Nst1ES 3189 augita macl 10
   Subtitle:
          Ag: Constituent name: Augite;
          Pl: Constituent name: Plagioclase;
          Ab: Constituent name: Albite;
          I: Constituent name: Illite;
   Purposes: Primary composition

   Description: Nst1ES 3189 veio sm plag 1
   Subtitle:
          Pl: Constituent name: Plagioclase;
          Gl: Constituent name: Mafic glass;
          Red Arrow: Constituent name: Nontronite - Habit: Sheaf - Location: Cavity-filling - Paragenetic relation: Fracturing of <Constituent> - Paragenetic relation constituent: Constituent undifferentiated;
   Purposes: Paragenetic relation, Deformation structure, Secondary composition

   Description: Nst1ES 3189 olivina 5
   Subtitle:
          Red Arrow: Constituent name: Serpentine - Location: Intracrystalline replacive - Paragenetic relation: Replacing <Constituent> - Paragenetic relation constituent: Olivine;
          Dark blue Arrow: Constituent name: Iddingsite - Location: Intracrystalline replacive - Paragenetic relation: Replacing <Constituent> - Paragenetic relation constituent: Olivine;
   Purposes: Paragenetic relation, Secondary composition

Microscopic textural features

    Structure(s): Massive
    Crystallinity: Hemicrystalline
   Granularity: Aphanitic
   Relative crystal size: Equigranular
   Modal grain size: (100.0 mm)
   Crystal size range: Very fine-grained (4.0E-4 mm) to Medium-grained (2.6 mm)
   Modal crystal size: Fine-grained (0.84 mm), Fine-grained (0.23 mm), Very fine-grained (0.06 mm)

    Crystal shape
        Perfection crystal shape: Idiomorphic
        Three-dimensional crystal shape: Prismatic

    Texture(s): Intergranular, Intersertal, Variolitic, Symplectitic

Composition
   37.33% Calcic plagioclase, Prismatic, As primary constituent, Twinned, Primary;
   11.67% Albite, Sheaf, Intercrystalline, Replacing <Constituent>, Mafic glass, Glass, Intercrystalline;
   1.67% Albite, Skeletal, Intercrystalline, Replacing <Constituent>, Mafic glass, Glass, Intercrystalline;
   28.33% Augite, Prismatic, As primary constituent, Twinned, Primary;
   2.33% Augite, Skeletal, As primary constituent, Intergrown with <Constituent>, Ilmenite, Other Oxides, As primary constituent;
   7.67% Mafic glass, Massive, Intercrystalline, Altered, Primary;
   4.67% Ilmenite, Skeletal, As primary constituent, Intergrown with <Constituent>, Augite, Pyroxenes-Pyroxenoids, As primary constituent;
   1.67% Ilmenite, Skeletal, Intercrystalline, Replacing <Constituent>, Mafic glass, Glass, Intercrystalline;
   1.0% Ilmenite, Microcrystalline, Interparticle, Covering <Constituent>, Augite, Pyroxenes-Pyroxenoids, As primary constituent;
   1.0% Ilmenite, Skeletal, As primary constituent, Intergrown with <Constituent>, Calcic plagioclase, Feldspars, As primary constituent;
   0.67% Calcite, Coarsely-crystalline, Intercrystalline, Replacing <Constituent>, Mafic glass, Glass, As primary constituent;
   0.67% Iddingsite, Microcrystalline, Intraparticle replacive, Replacing <Constituent>, Olivine, Olivines, As primary constituent;
   0.67% Serpentine, Microcrystalline, Intraparticle replacive, Replacing <Constituent>, Olivine, Olivines, As primary constituent;
   0.33% Nontronite, Microcrystalline, Rock fracture-filling, Fracturing of <Constituent>, Constituent undifferentiated, Other constituents;
   0.33% Nontronite, Microcrystalline, Intraparticle replacive, Replacing <Constituent>, Olivine, Olivines, As primary constituent;

Classification

   Streckeisen - Plutonic Present: Gabbro
       Q: 0.0
       A: 0.0
       P: 100.0
       F: 0.0

   Streckeisen - Plutonic Original: Gabbro
       Q: 0.0
       A: 0.0
       P: 100.0
       F: 0.0

   Streckeisen - Volcanic Original: Basalt
       Q: 0.0
       A: 0.0
       P: 100.0
       F: 0.0

   Streckeisen - Volcanic Present: Basalt
       Q: 0.0
       A: 0.0
       P: 100.0
       F: 0.0

Total

Silicate	82.667
Non-Silicate	17.333
Porosity	0.0
Felsic minerals	50.667
Maphic minerals	39.667

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