One commenter suggested placing a small drop of vinegar on the specimen. Bubbling could indicate calcite. This was a tentative identification suggestion, not a confirmed identification.

The existing community answer is a useful but explicitly tentative clue, not a confirmed identification.[1] It reports that bubbling after a small vinegar drop could point toward calcite, but the current public question still does not establish the identity of either the white material or the shiny grey material.[1][unverified]

What fizz means

The University of Minnesota’s mineral reference explains that calcite and aragonite react with dilute acid, while quartz does not; that reaction is useful as one observation, not as a complete identification.[3] A fizz therefore can support the possibility of carbonate material, but it does not prove that the specimen is calcite or explain every part of a mixed rock.[unverified]

Compare carefully

BancroftOntario’s local guide describes calcite as commonly white, grey or colourless and lists many other local-region comparison minerals with different lustres, colours and habits.[2] “Softer than quartz” and “shiny grey” are not enough to choose among them without a clear specimen image, crystal habit, cleavage, streak and provenance.[unverified]

Safer next step

Do not break, grind or acid-test a potentially valuable, fragile or hazardous specimen merely to pursue an online identification.[unverified] Instead, photograph the whole rock and close-ups in neutral light, include a scale, record approximate size and weight, preserve any label or collecting information, and ask a mineral specialist to review it.[unverified]

The Bancroft Mineral Museum is the most relevant local first contact, although its published page does not promise a walk-in identification service.[4][unverified] The 2026 Rockhound Gemboree also documented expert mineral identification by Canadian Museum of Nature and Laurentian University specialists; that event has passed, so confirm the next programme before planning around it.[5][unverified]

Bottom line: keep the vinegar suggestion labelled as a preliminary carbonate clue only. No reliable species-level identification can be made from the current description alone.[unverified]

Sources

1. Ask Bancroft
2. Mineral descriptions
3. University of Minnesota
4. Mineral Museum
5. Gemboree identification

## Sources

[1] https://bancroftontario.com/ask-bancroft/question/can-someone-identify-a-white-crystal-like-rock-with-shiny-grey-material — Ask Bancroft question
[2] https://bancroftontario.com/mineral-descriptions-2 — BancroftOntario mineral descriptions
[3] https://commonminerals.esci.umn.edu/minerals-f/calcite-and-aragonite — University of Minnesota calcite reference
[4] https://bancroftontario.com/bancroft-attractions/bancroft-mineral-museum — Bancroft Mineral Museum
[5] https://www.bancroftrockhoundgemboree.ca/things-to-do — Rockhound Gemboree identification