sedimentary

Milky Quartz in Conglomerate Matrix

Silicon Dioxide (SiO2) within Clastic Sedimentary Rock

AI-generated identification · may be incorrect

Hardness: 7 (Mohs scale), Color: White to grayish-blue quartz with reddish-brown sandy matrix, Luster: Vitreous to dull, Structure: Hexagonal crystal system (microcrystalline in this form), Cleavage: Indistinct/Conchoidal fracture

Identified February 19, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the accumulation of weathered rock fragments and quartz pebbles that were cemented together by silica or iron oxide in high-energy fluvial (river) or marine environments. The quartz itself likely formed via hydrothermal veins millions of years prior to being eroded and redeposited into the sedimentary conglomerate unit.

Uses & applications

Primarily used as construction aggregate or road base material. Larger conglomerate stones are used for decorative landscaping and as historical markers in architectural foundations.

Geological facts

Quartz is the second most abundant mineral in Earth's continental crust. Conglomerates like this are often referred to as 'pudding stones' when the contrast between the pebbles and the matrix is particularly sharp.

Field identification & locations

Identify in the field by looking for rounded or sub-angular pebbles embedded in a finer-grained sandy 'cement.' It will feel heavy and coarse. Commonly found in old riverbeds, glacial till, and coastal cliffs. Scratch testing the white parts with steel should leave no mark, indicating high hardness.