# O/C Isotopic and EPR Signature of Marble from the Apuan Alps (Italy): A Critical Review
## 2 Material and Methods
### Geological Setting
#### 2.1.3 Characteristic of the AAMs  
Under transmission optical microscope (TOM) analysis, AAMs show a homeoblastic grano-xenoblastic texture, grain size ranging from 0.1 to 0.8 mm, sutured and indented grain boundaries, relics of twins and glide surfaces and sub-grain partitioning in the largergrains (>0.6 mm). New crystals free of strain have linear sharp boundaries and polygonal shapes [18]. All these features are differently distributed in the AAM lithotypes:  
_Marno dolomite:_ Dolomite is abundant, has a rhombohedral habit, ranges in size from 0.2 to 0.4 mm of diameter and shows sharp boundaries. In the marble layers, calcite has an average grain size of 0.1 mm; in this lithotype, there are also regions with larger calcite crystals (0.3 to 0.8 mm) containing twins and gliding surfaces. Calcite grain size decreases to micro-crystalline (<0.05 mm) where there are dolomite or second-phase particles. Boundaries are indented or sutured towards the Venato Forte and become progressively curved or gently curved toward the Venato. _Venato forte:_ Venato appears strongly heterogeneous in crystal size, ranging from <0.3 to 0.5 mm; some regions, aligned in the verso, are characterised by the presence of twinned crystals whose size is larger than average (0.2 to 0.3 mm). The grey bands aligned in the verso number particles of additional phases and the presence of regions of calcite micro-crystals (<0.01 mm) comprising totally, or in part, the grey veins. Dolomite is present as rhombohedral crystals close to phyllosilicate layers, ranges from 0.1 to 0.2 mm and in some cases possesses a core and rim structure. Phyllosilicates (white mica and chlorite) are widespread in the calcite matrix or concentrated in sub-millimetric layers within which there are abundant particles of accessory minerals with a 0.01 mm average diameter. Phyllosilicates are dimensionally elongated in the main schistosity and behave as strong fibres driving the shape of calcite, whose boundaries in this case are always very sharp and straight. _Venato:_ Calcite crystals range from 0.1 to 0.4 mm with boundaries gently concavely curved outwards or sharp and polygonal in the smaller ones. Laying parallel with the main schistosity, regions of larger calcite crystals (0.4 to 0.8 mm) occur, where calcite presents twins and gliding surfaces and indented or sutured boundaries. Veins result, enriched in dolomite and additional minerals. Dolomite crystals are generally larger than calcite ones and isolated from each other. Their boundaries are sharp, and rhombohedral gliding planes can be present. _Venato:_ Calcite crystals have the same features as the Venato, but sizes are clustered at 0.2-0.4 mm and relics of twinning and gliding surfaces become rare. Dolomite crystals are rare, but always with a rhombohedral habit. _Breccia:_ The matrix appears to be formed by very small calcite crystals (<0.05 mm), accessory mineral particles and rarer dolomite with a rhombohedral habit (size 0.2-0.3 mm). Clasts consist of calcite crystals, with sizes ranging from 0.2 to 0.4 mm, which have the same features as in the _Venato_. _Ordinario and Statuario_: They consist exclusively of calcite crystals, whose sizes are clustered around the mean (from 0.3 to 0.8 mm). Relics of twins and glide surfaces are common. Calcite crystals often show bands of light undulated extinction; the boundaries are fairly sharp but indented. _Bardiglio:_ Calcite crystals have sizes from 0.05 to 0.1 mm in the dark grey background, whereas they range from 0.2 to 0.4 mm in the white stains; quartz is present even if in very small amounts. The authors of [21; 22] analysed several lithological sections across the AAMs and related the main AAM types to the carbonate-platform facies on the basis of grain sizes and texture (Table 1). Back-folding the Apuan Alps tectonic edifice [21; 22] obtained a thickness for the AAMs of about 200 m, as for the Calcare Massiccio protoolith of the overlying Tuscan Nappe.