How Difficult is it to Break Bedrock? Understanding the Variation in Hardness

Sandstone Bedrock

Sandstone consists of grains of quartz that are loosely or firmly cemented together. Depending on the cementation, sandstone can range from very soft to quite resistant. Unconsolidated sand can almost be considered a loose granular material rather than true bedrock. With little force, grains of sand can be rubbed away with fingers. Weakly cemented sandstone only requires minor effort with a hammer or pick to break apart. However, more lithified sandstone becomes progressively harder to fracture as the cementation increases. Strongly cemented sandstone needs more substantial tools like a pickaxe or hammer and chisel to break pieces off the outcrop.

Chalk and Limestone Bedrock

As carbonate bedrock, both chalk and limestone are soluble in weak acids like the carbonic acid found in rainwater. Over thousands of years, this natural weathering process can leave these rocks highly fractured and jointed. Impure chalk may be relatively soft and can snap apart easily with bare hands. Almost flour-like chalk powder can rub off the outcrop surface. Pure chalk becomes denser but still fractures quite readily using simple hand tools. Similarly, oolitic or bioclastic limestones often break along fossil or grain boundaries. More crystalline limestones prove tougher to fracture manually due to smaller pore spaces and less weathering along defects. Generally, limestones require a hammer or geological pick to extract samples.

Clay Bedrock

Clays derive from the chemical weathering and breakdown of various parent rocks over geologic time. Their composition depends on the minerals in the parent material. So their hardness spans quite a range. London clay formed from eroded Tertiary-age sediments is quite soft and can slice readily using a sharp trowel or spade. Other continental clays may prove tougher, requiring a geology hammer to split apart. Highly altered clays containing montmorillonite can become quite weak thanks to expansion and contraction with moisture changes. Marine clays may indurate more strongly, necessitating hammer and chisel use. Overall, clays fall at the softer end of the bedrock hardness spectrum.

Igneous and Metamorphic Bedrock

Igneous and metamorphic rocks solidified or recrystallized under high pressures and temperatures, rendering most quite resistant to breaking compared to sedimentary varieties. Cooling joints or shear zones serve as potential planes of weakness. Coarse-grained granites and gabbros prove exceptionally difficult to manually fracture without steel tools like a hammer and chisel or small geology pick. Perhaps only weathered surface crusts may flake away. More porous andesite or fine-grained equivalents could split somewhat using heavy hammer blows. Metamorphic rocks like gneiss or marble contain strongly bonded crystals, demanding significant force to crack or chip. Gabbro, basalt, and quartzite rank among the hardest rocks to manually sample without machinery like a coring drill.

Bedrock Difficulty and Geological Structure

While mineral and chemical composition establishes a baseline hardness, geological structure also influences how demanding it is to fracture bedrock. Massive or featureless rocks lack weaknesses for stresses to propagate through. Well-jointed, faulted, or foliated bedrock provides natural fracturing along which stresses more readily travel. Coastal or mountainous regions commonly exhibit high degrees of jointing or faulting through tectonic stresses or glacial unloading during past ice ages. This structural guidance lowers the effort required compared to massively bedded equivalents. Also, variable cementation across a formation introduces inconsistency in resisting breakage. In summary, assessing lithology alone cannot determine bedrock difficulty - fabric significantly moderates hard-won manual sampling.

Laboratory Experiments Inform Field Observations

To quantify rock strength objectively, material scientists conduct standardized compression tests in the lab. Applying calibrated axial loading reveals the unconfined compressive strength (UCS) of intact specimens. Texturally homogenous igneous rocks often reach 100s of MPa while soft sedimentary varieties may fall in the 1-10 MPa range. However, in situ field conditions introduce more variables than clean laboratory pressure. Pre-existing fractures, weathering rinds, oriented fabrics, and dynamic stresses all act to potentially lower the force needed compared to fresh lab samples. Still, UCS values provide a useful guide for roughly classifying global bedrock hardness when selecting fieldwork tools or rating excavation difficulty for construction projects.

Predicting Breakage Effort in the Field

Synthesizing available contextual clues helps forecast breakability challenges during fieldwork. Bedrock mapping denotes broad lithology while outcrop character reveals textures and structures. Samples or previous descriptions supply mineralogical and fabric details. Sedimentary indicators like grains, fossils or bedding imply the depositional environment. Certain metamorphic grades also specify conditions of formation. Previous quarrying history hints at a rock’s amenability to productive shaping via machinery versus hand tools. An understanding of typical weathering styles aids recognizing altered surfaces. Weighing all obtainable geological intelligence facilitates preparedness for forecasting bedrock breakage effort during field investigations and sampling. Proper precautions likewise safeguard researchers from preventable mishaps or wasted time battling obdurate outcrops.

Safety First When Breaking Bedrock

No matter how meticulously prepared, many unknowns remain in the field. Thus safety shall override ambition when manually fracturing bedrock. Intimate knowledge of local geology informs hazards arising from features like shear zones prone to sliding. Adequate personal protection equipment (PPE) like eye protection, steel-toe boots, and gloves protects against flying fragments. Always keeping hands clear while firmly bracing samples averts injuries from uncontrolled cracking. Watchful positioning upslope safeguards individuals from unintended rockfalls sourced uphill. Fitness helps avoid overexertions that cause slips or strains when exerting high force. If breakage proves too difficult or unstable, retreat and reassess tactics to complete tasks without compromising wellbeing. Overall, adopting a prudent, considered approach optimized for each outcrop situation optimizes academic benefit alongside safety. In summary, bedrock hardness exhibits high variability depending on lithology, fabric, weathering, and geologic context. However, diligent review of contextual clues regarding formation, structure, and materials allows characterizing resistance to breakage during fieldwork. Proper precautions further ensure breaking samples proceeds without unacceptable risks to researchers’ wellbeing. Knowledge, preparation, and careful technique help unlock insights from the rock record with both efficiency and safety.