The quality or state of being brittle or easily broken, as bricks would be.
From the adjective 'brickle' plus the suffix '-ness', which converts adjectives to abstract nouns describing qualities. This follows the standard pattern for English noun formation.
The 'brickleness' of fired clay was actually crucial to medieval builders—slightly brittle bricks would shatter under stress rather than crushing through an entire wall, which inadvertently improved structural safety.
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