Rock Tumbling Time Requirements by Material

Agate rough entering a tumbler on January 1st emerges polished on January 28th. Obsidian starting the same day finishes January 18th. Beryl loaded alongside both won't be ready until mid-March. Same tumbler, same grit quantities, same operator. The only variable: material hardness dictating calendar reality. A hobby tumbler running continuously processes roughly 13 standard batches of agate per year. That same machine handles perhaps 8 batches of beryl. The calendar math shapes every decision about what materials justify the time investment.

The standard four-week tumbling cycle (7 days per stage across four stages) applies specifically to materials rating 7 on the Mohs hardness scale. Quartz, agate, jasper, and petrified wood all cluster at this hardness and complete predictably in 28 days. Materials softer than 7 finish faster. Materials harder than 7 require extended processing. The time differences compound across all four stages, creating substantial calendar variations between material types.

The Standard 28-Day Cycle: Mohs 7 Materials

Agate represents the benchmark tumbling material. Most commercially sold tumbling rough consists of Brazilian or Mexican agate for good reason—the material processes reliably on the standard cycle. Starting with properly sized rough (3/8 to 1-1/4 inches for small tumblers), agate completes coarse grinding in 7 days, medium grinding in 7 days, fine grinding in 7 days, and polishing in 7 days. Total elapsed time: 28 days from rough to finished.

Jasper follows identical timing. Red jasper, picture jasper, ocean jasper, and other varieties all rate approximately 7 on Mohs and complete in four weeks. The opacity makes visual progress assessment slightly more difficult than with translucent agate, but processing duration remains consistent. Some jasper types with higher clay content or softer inclusions complete marginally faster—perhaps 25 to 26 days total—but the variation stays within a few days of the standard cycle.

Quartz varieties including amethyst, citrine, smoky quartz, and rose quartz also complete in 28 days when properly sized. Clear quartz crystals larger than an inch require careful handling to prevent fracture but follow the same time schedule. The transparency allows easy progress monitoring throughout the cycle—after coarse grinding, the stones show obvious rounding; after medium, they begin developing luster; after fine, they approach final smoothness.

Petrified wood completes on the standard schedule when the replacement mineral consists of chalcedony or jasper (the most common types). The organic structure creates slightly different grinding patterns than pure mineral stones, sometimes leaving subtle texture, but overall processing time remains 28 days. Wood specimens with heavy weathering or partially replaced structure may require extended coarse grinding—perhaps 10 days instead of 7—to achieve acceptable shaping.

Carnelian and other chalcedony varieties process similarly to agate since they represent the same basic material with different coloring. Tiger's eye, technically a quartz variety with fibrous structure, completes in 28 days but benefits from slightly gentler tumbling to prevent edge bruising. The chatoyant effect (the "eye" created by fibrous crystals) remains intact through standard processing.

Accelerated Processing: Mohs 5-6.5 Materials

Feldspar family stones including moonstone, sunstone, amazonite, and labradorite all rate approximately 6 to 6.5 on Mohs and complete faster than the standard cycle. The reduced hardness means grit cuts more efficiently, requiring less calendar time per stage. Typical feldspar processing: 5 days coarse, 5 days medium, 5 days fine, 5 days polish. Total time: 20 days from rough to finished.

The ten-day reduction from standard agate timing adds up quickly when running multiple batches. A tumbler processing feldspar exclusively completes roughly 18 batches per year compared to 13 agate batches—a 38% increase in throughput. The economic calculation matters for anyone purchasing rough regularly or running commercial operations.

Unakite (a granite composed primarily of feldspar, epidote, and quartz) follows similar timing despite technically representing a rock rather than a single mineral. The mixed hardnesses average to approximately 6 to 6.5, matching pure feldspar processing times. The mottled green and pink coloring develops attractive polish in the standard 20-day feldspar cycle.

Obsidian at Mohs 5 to 5.5 processes even faster. The volcanic glass lacks crystalline structure, allowing rapid grinding. Typical obsidian timing: 3 to 4 days coarse, 4 to 5 days medium, 4 to 5 days fine, 5 to 6 days polish. Total time: 16 to 20 days depending on piece size and desired final size. Larger obsidian pieces benefit from the longer end of this range. Smaller pieces complete successfully at the shorter duration.

The reduced processing time creates a secondary consideration: obsidian pieces shrink substantially during tumbling due to rapid material removal. A one-inch obsidian nodule might emerge as a 5/8-inch finished stone after the accelerated cycle. Starting with slightly larger rough compensates for this material loss. The alternative—tumbling obsidian for the full standard 28-day cycle—produces tiny finished stones with excessive material waste.

Sodalite rates 5.5 to 6 on Mohs and processes on a schedule between obsidian and feldspar. Typical timing: 4 days coarse, 5 days medium, 5 days fine, 6 days polish. Total time: 20 days. The rich blue color develops excellent luster in this timeframe. Extended processing beyond 20 days provides minimal improvement while increasing material loss unnecessarily.

Turquoise presents variable timing based on hardness and porosity. Natural turquoise ranging from Mohs 5 to 6 typically requires 18 to 22 days total. Stabilized turquoise (resin-impregnated to fill pores) often processes successfully in 20 to 24 days. The stabilization adds structural integrity, allowing slightly longer processing without excessive material loss. Natural porous turquoise requires the shorter timeframes to prevent over-grinding.

Extended Processing: Mohs 7.5-9 Materials

Materials harder than 7 require extended processing at every stage. The calendar multiplication becomes significant—a material requiring 10 days per stage instead of 7 extends the total cycle from 28 to 40 days. The twelve-day difference means three fewer batches per year per tumbler.

Beryl family stones (emerald, aquamarine, morganite) rate 7.5 to 8 on Mohs. Typical beryl timing: 10 to 14 days coarse, 10 days medium, 10 days fine, 7 to 10 days polish. Total time: 37 to 44 days for most specimens. Particularly hard emerald pieces sometimes require the full 14-day coarse cycle while softer morganite might complete in 37 days. The variation depends on specific chemical composition and crystal quality.

The extended timeline creates opportunity cost calculations. A tumbler dedicated to beryl for 42 days could have processed 1.5 batches of agate in the same period. The decision requires weighing raw material costs against finished stone value. Beryl rough typically costs $8 to $15 per pound compared to $2 to $5 per pound for agate. The finished stones command proportionally higher prices, but the time investment must justify the markup.

Topaz at Mohs 8 pushes processing times further. Typical topaz timing: 14 to 21 days coarse, 10 to 14 days medium, 10 days fine, 7 to 10 days polish. Total time: 41 to 55 days. The variability depends on topaz color and clarity—blue topaz generally processes toward the faster end while imperial topaz requires maximum duration. Some operators report running topaz coarse grinding for three full weeks to achieve acceptable rounding.

Garnet varieties show substantial timing variation based on specific type. Almandine garnet (the common red type) rates 7 to 7.5 and processes in 30 to 35 days. Pyrope and rhodolite garnet rate slightly higher at 7.5 and require 35 to 40 days. Grossular garnet (including tsavorite and hessonite) rates 7 to 7.5 with processing times matching almandine. The differences remain subtle enough that mixed garnet batches can tumble together successfully using a 35-day schedule.

Corundum (ruby and sapphire) at Mohs 9 enters impractical territory for hobby tumbling. Processing times extend to 8 to 12 weeks or longer. Typical corundum timing when attempted: 6 to 8 weeks coarse, 2 to 3 weeks medium, 2 weeks fine, 1 to 2 weeks polish. Total time: 11 to 15 weeks. The extended coarse grinding accounts for most of the duration—the material's hardness means silicon carbide grit cuts extremely slowly. Many operators abandon corundum tumbling after initial experiments, finding the time investment unjustifiable.

Calendar Planning for Mixed Hardness

Running multiple tumblers with different materials simultaneously requires calendar coordination. Starting an agate batch and a feldspar batch on the same day creates staggered completion. The feldspar finishes around day 20. The agate continues until day 28. Loading a new feldspar batch immediately creates an 8-day offset between the two machines.

The offset multiplies across subsequent batches. After three cycles, the feldspar tumbler has completed four batches while the agate tumbler completed three. The scheduling works smoothly until vacation planning or extended absence becomes necessary. Stopping all tumblers simultaneously for a two-week vacation requires coordinating start dates carefully—loading batches that will complete just before departure rather than mid-cycle during absence.

Some operators synchronize all batches to standard 7-day stage intervals regardless of material hardness. A feldspar batch might run 7 days per stage (28 days total) instead of the optimal 5 days per stage (20 days). The extended processing provides no benefit—the stones reach final smoothness by day 20 and the additional 8 days simply wastes electricity. But the synchronized schedule simplifies planning when running multiple machines.

The alternative approach dedicates specific tumblers to specific material types. One machine runs agate continuously on 28-day cycles. A second machine runs feldspar on 20-day cycles. A third handles obsidian on 18-day cycles. Each machine maintains its own schedule without coordination requirements. The batch completion dates vary but the system operates independently.

Seasonal Considerations

Ambient temperature affects processing times marginally. Summer heat accelerates chemical reactions and grit breakdown, sometimes reducing required stage duration by half a day. Winter cold slows these processes, occasionally warranting an extra half-day per stage. The effect remains subtle—perhaps 26 days total in summer versus 30 days in winter for the same agate batch.

Most operators ignore seasonal variation since it falls within normal batch-to-batch variation from other factors (rough quality, grit freshness, barrel loading density). Commercial operations running climate-controlled facilities eliminate seasonal effects entirely. Hobby operators in unheated garage spaces notice the winter slowdown but rarely adjust schedules formally.

Extended power outages disrupt tumbling schedules unpredictably. A tumbler stopped mid-coarse-grind for 24 hours during a winter storm requires assessment. The grit settles to the barrel bottom. The stones sit stationary against each other. Restarting after the outage resumes processing but the interrupted day doesn't count toward the 7-day cycle. Most operators add an extra day to any stage experiencing significant interruption.

Monitoring Progress and Adjusting Duration

Opening the barrel mid-stage for progress inspection adds minimal time impact—perhaps 30 minutes for washing a sample stone, examining it, and reloading the barrel. The lost tumbling time becomes negligible across a 168-hour stage. Operators working with unfamiliar materials often inspect at day 5 of a planned 7-day coarse stage to assess whether extension appears necessary.

The inspection reveals physical progress. Stones that still show sharp edges or significant flat spots after 5 days probably need 10 to 14 days total in coarse grit. Stones that appear adequately rounded by day 5 might complete acceptably at 6 days rather than the full 7. The adjustment prevents over-processing faster materials while ensuring thorough processing of harder materials.

Some operators weigh sample stones at stage completion to calculate material loss. An agate stone starting at 100 grams typically finishes around 70 to 80 grams after four complete stages—20 to 30% total loss. Obsidian might show 35 to 45% loss due to faster grinding rates. Beryl might show only 15 to 20% loss due to slower grinding. These measurements inform future batch planning for specific materials.

Throughput Calculations

A single rotary tumbler operating continuously processes 13 standard agate batches annually. Each batch requires 28 days start to finish. Accounting for barrel cleaning, stone sorting, and grit changes between batches adds roughly half a day per cycle. Total time per batch: 28.5 days. Annual capacity: 365 days ÷ 28.5 days per batch = 12.8 batches, rounded to 13.

The same tumbler running obsidian exclusively processes 19 batches annually. Each obsidian batch requires 18 days plus half-day transition. Total: 18.5 days per batch. Annual capacity: 365 ÷ 18.5 = 19.7 batches, rounded to 20.

Running beryl reduces throughput to 8 batches annually. Each beryl batch requires 42 days plus half-day transition. Total: 42.5 days per batch. Annual capacity: 365 ÷ 42.5 = 8.6 batches, rounded to 9.

These calculations assume continuous operation with no extended downtime. Real-world operations experience maintenance needs, vacation periods, and time gaps between obtaining new rough. Actual annual throughput typically runs 10 to 12 batches for agate, 15 to 18 for obsidian, and 6 to 8 for beryl.

Economic Impact of Processing Duration

Material costs per finished pound vary substantially based on processing time. Agate rough costs approximately $2 to $5 per pound. Processing costs (grit, polish, electricity) add $3 to $5 per finished pound. Total investment: $5 to $10 per finished pound. Market value of quality tumbled agate: $12 to $25 per pound. Processing time: 28 days.

Beryl rough costs $8 to $15 per pound. Processing costs add $8 to $12 per finished pound due to extended cycle time and increased consumable usage. Total investment: $16 to $27 per finished pound. Market value of tumbled beryl: $30 to $60 per pound. Processing time: 42 days.

The profit margin percentages look similar—roughly 100 to 150% markup for both materials. The calendar economics differ dramatically. Processing agate generates approximately $7 to $15 profit per pound every 28 days. Processing beryl generates $14 to $33 profit per pound every 42 days. The per-day profit rate actually favors agate: $0.25 to $0.54 per pound per day versus $0.33 to $0.79 per pound per day for beryl.

These calculations ignore hobby operator realities—most tumble for enjoyment rather than profit. But the economics explain why commercial operations focus on standard 28-day materials. The throughput advantage compounds across multiple tumblers.

Batch Scheduling Strategies

Sequential processing runs one batch to completion before starting the next. This approach suits single-tumbler operations or materials with similar processing times. All equipment stays synchronized. The operator manages one set of dates and transitions.

Staggered processing starts batches at regular intervals regardless of completion dates. A two-tumbler operation might start a new batch every 14 days—tumbler one starts January 1st and January 29th; tumbler two starts January 15th and February 12th. This creates regular workflow without idle equipment. The strategy works well when processing consistent materials on known schedules.

Flexible processing starts new batches as tumblers become available without fixed scheduling. This approach handles mixed materials and varying processing times naturally but requires more attention to tracking. The operator maintains a list of completed and in-progress batches rather than following a calendar schedule.

Reality of Processing Time Variation

Published processing times represent averages across typical conditions. Individual batches show variation based on rough quality, grit freshness, barrel loading density, tumbler speed, and material-specific characteristics beyond hardness ratings. An agate batch might complete exceptionally well in 25 days or require 32 days to achieve comparable results.

The variation prevents overly precise scheduling. Planning based on 28-day standard cycles works reliably for agate but building in 2 to 3 days flexibility prevents disappointment when specific batches require extension. Experienced operators develop intuition about when extension makes sense versus when results are satisfactory despite falling slightly short of theoretical perfection.

Calendar planning matters most when deadlines exist—completing stones for a specific show, filling an order by a promised date, or finishing before scheduled absences. Under normal circumstances, the batch completes when it completes. The stones don't care about calendars.

Related: Rock Tumbling Grit Progression Explained, What Rocks Can Be Tumbled: Mohs Hardness Guide, The Best Rock Tumbler